Welcome to the latest in our new feature where we look back at the most important comic book #1s of each decade. We're continuing with 2000-2009, the first decade of the current century!

RELATED: Number Ones: The Most Important #1 Issues (2010 - Today)

The 2000s saw a seismic shift at both Marvel and DC Comics, as Marvel launched a very important line of comics and DC dramatically changed their image. There were important issues outside of the "Big Two," as well, including the launch of a comic book phenomena. We're just talking the first issues of series here, remember, so graphic novels aren't eligible for this list. Here, then, are the 15 most important #1 issues of 2000-2009, the first decade of the 21st Century!

15 Buffy The Vampire Slayer: Season Eight #1

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Screenwriter Joss Whedon had already made a big impression on the comic book world with his run on "Astonishing X-Men" with artist John Cassaday ("Astonishing X-Men" #1 nearly made this countdown on its own) and in his story of what vampire slaying is like in the future with the mini-series "Fray," but his biggest impact on the comic book market was likely when he launched "Buffy the Vampire Slayer Season Eight" at Dark Horse Comics in 2007.

Drawn by Georges Jeanty, the series continued the story of Whedon's acclaimed TV series, "Buffy the Vampire Slayer," from where the original show ended, and since it was written by the show's creator, the stories had an extra "official" air to them. The success of this project led to many other comic book companies deciding to continue other older television series as comic books, from "X-Files: Season 11" to "Batman '66". In addition, the TV writing staff approach (where Joss Whedon oversees the writing, but other writers actually script each individual issue after Whedon's initial story arc) has been tried a few times since by other comic book creators, from "Avengers vs. X-Men" to "Thief of Thieves."

14 Annihilation: Conquest - Star-Lord #1

Star-Lord, guns blazing, from Annihilation: Conquest in Marvel Comics

The reclamation of Marvel's Cosmic heroes had already begun in 2005 when Keith Giffen came up with a new take on Drax the Destroyer in a "Drax the Destroyer" mini-series. That followed Giffen bringing Star-Lord back in his 2004 stint on "Thanos" after Jim Starlin left the title, as well as predated Giffen bringing Groot back to the Marvel Universe in his 2005 series, "Nick Fury and His Howling Commandos." "Drax" led directly into the 2006 crossover event, "Annihilation."

In 2007, there was a sequel crossover called "Annihilation: Conquest." This time, Dan Abnett and Andy Lanning were handling the main event, but Giffen wrote a prelude mini-series called "Annihilation: Conquest - Star-Lord" with artist Tim Green III. The series saw Star-Lord forced to put together a sort of suicide squad made up of disparate Marvel Cosmic characters, including (working together for the first time) Rocket Raccoon and Groot. Following "Annihilation: Conquest," Star-Lord, Rocket and Groot all joined Abnett and Lanning's "Guardians of the Galaxy" spin-off series, which in turn inspired the blockbuster film franchise.

13 Y The Last Man #1

Y: The Last Man ends with a conversation between an elderly Yorick and his younger self

In 2000, DC Comics gave two up-and-coming Vertigo writers a shot at replacing Larry Hama on "Batman." Ed Brubaker and Brian K. Vaughan were each given tryout arcs. Brubaker's arc came out first and it was so well-received that he was hired on as the book's regular writer before it had even finished! Vaughan's arc then came out and it was excellent, as well, but the die had already been cast. At the time, you couldn't help but feel a little bad for Vaughan. Then "Y The Last Man" #1 came out in 2002 and Vaughan's whole career changed.

The epic series about the last man on Earth and his quest to help a scientist figure out if she can bring men back before the human race dies out was a huge hit for Vertigo, giving them their first big success since "Preacher" ended in 2000. It also let everyone know how great of a writer Brian K. Vaughan was. Marvel gave him two series the following year, including his co-creation, "Runaways." He then launched "Ex Machina" for Wildstorm and got into TV writing. Today, he is one of the most acclaimed writers in the comic book industry, writing his creator-owned series "Saga" and "Paper Girl" for Image Comics, and it all really started with this issue.

12 Iron Man #1

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Following "Avengers Disassembled," the various "Avengers"-related titles all had notable relaunches in 2005. "Iron Man" was relaunched by writer Warren Ellis and artist Adi Granov with a story arc called "Extremis." In the story, Tony Stark injects himself with Extremis, a nanotechnological "virus" that, in effect, turns him into an actual Iron Man, as his armor becomes basically part of his own body.

The 2008 blockbuster film, "Iron Man", relied heavily on "Extremis" for their take on the character of Iron Man, specifically hiring Adi Granov as a producer on the film and having him produce the final design the armor used in the film. In addition, the film adapted Ellis' new origin for Iron Man pretty closely. The entire plot of "Extremis" was later adapted for the third "Iron Man" film. One storyline inspiring two separate hit movies? Not bad for a single arc on a comic book series!

11 30 Days of Night #1

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Steve Niles' pitch for "30 Days of Night" was one of the all-time great elevator pitches, as a small town in Alaska has to deal with being attacked by vampires during the time of the year where it is dark all month long. However, for whatever reason, he could not sell his movie script. He later recalled, "I pitched it to just blank faces. And they'd say, 'It sounds like Buffy, it sounds like Buffy.' And honestly I had just about given up." However, Niles had been writing comic books for a while at the time, so he took his script and made it into a comic book series at the newly launched company, IDW, in 2002, drawn by Ben Templesmith.

The series was a huge hit and suddenly, movie studios that had ignored the story as a screenplay were breaking down the doors trying to buy the movie rights from Niles. The project then stood out for a whole new realm of comic books designed to be adapted into films and television series. Mark Millar, in particular, has had great success getting his original ideas picked up for films, like 2003's "Wanted" and 2008's "Kick-Ass".

10 JLA/Avengers #1

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In 1982, Marvel and DC were riding high off of a series of successful comic book crossovers, from "Superman/Spider-Man" to "Batman vs. the Incredible Hulk" to "X-Men/New Teen Titans". The next crossover was going to be a "JLA/Avengers" crossover drawn by George Perez, the only man at the time to have been the regular artist on both titles. However, in a disagreement that is still being disputed over 30 years later concerning who was to blame for the argument, the crossover fell apart and DC and Marvel called off all future crossovers (this would remain the case for over a decade).

Therefore, when Kurt Busiek (who also had worked on both titles) and George Perez finally released "JLA/Avengers" in 2003, it was a historic achievement, and not just because it is the last time that the two companies put out a crossover together, but just for the sense of closure that happened when the great George Perez got to finish what he had started two decades earlier. Plus, of course, a crossover between the Justice League and the Avengers is a big deal either way!

9 Alias #1

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In 2001, Marvel launched their MAX line of books, comic books intended for adults only. The first book in the series was "Alias" by Brian Michael Bendis and Michael Gaydos. The series introduced the world to private investigator and former superhero, Jessica Jones.

The first issue caused a lot of controversy, as it has a relatively graphic sex scene in it between Jones and Luke Cage. The issue ran afoul of Marvel's printer in Alabama, American Color Graphics, who refused to print the comic book due to the issue's "offensive material." There has been a lot of debate over the years on what was offensive about the material - that it showed sex at all? That it showed sex between a white woman and a black man? That it depicted anal sex? All of the above?

"Alias" would become a cult classic and the character of Jessica Jones obviously went on to big things, starring in her own hit Netflix TV series last year.

8 Green Lantern: Rebirth #1

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Writer Geoff Johns had begun to take on more and more prominence at DC Comics beginning in the late 1990s (in one of his earliest works at DC, he wrote the 1999 crossover "Day of Judgment," where Hal Jordan became the new Spectre) and early 2000s, as he became the writer of "JSA" and "Flash" right around the same time in 2000. In 2003, he relaunched "Teen Titans" as a mixture of the classic "New Teen Titans" lineup with the "Young Justice" lineup.

In 2004, though, he did his most famous work of the time, when he brought Hal Jordan back as Green Lantern, as well as the entire Green Lantern Corps in "Green Lantern Rebirth" (along with artists Ethan Van Sciver and Prentis Rollins). Not only did this lead to a revitalized "Green Lantern" series (Johns would go on to write "Green Lantern" for nearly a decade) and help inspire the 2011 "Green Lantern" motion picture, but it also worked as a new approach for DC Comics, where they began to downplay their legacy heroes in favor of spotlighting the "classic" versions of their main characters. First, Hal Jordan and then later "Flash Rebirth" (also by Johns) which re-established Barry Allen as the Flash.

7 Captain America #1

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For years, there had been four comic book characters whose deaths seemed to be set in stone: Uncle Ben Parker, Gwen Stacy, Mar-Vell and Bucky Barnes. Editor Tom Brevoort was going to make sure it stayed that way, as he had already turned down a recent request to bring Bucky back from the dead. However, Ed Brubaker was up to the task.

"Captain America" was one of a handful of titles that relaunched in the wake of "Avengers Disassembled." Brubaker had an idea involving bringing Bucky back from the dead. Brevoort grilled him with a series of questions as to why this would be a good idea for Marvel. Shockingly, Brubaker answered them all and Brevoort admitted that his idea worked, so they went forward with the "Winter Soldier," revealing that Bucky Barnes had survived all these decades, having been brainwashed into serving as an assassin for the Soviets. The Soviets would put him into cryogenic storage between missions, so he had barely aged in the 60 years since they found him (hence the name, "Winter Soldier").

While the return of the Winter Soldier (which was adapted into the hit film, "Captain America: Winter Soldier") is notable enough to be here, this was also the launch of a very acclaimed run on "Captain America" by Brubaker and artists Steve Epting and Mike Perkins.

6 Civil War #1

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Right from the first issue, it was clear that Mark Millar, Steve McNiven and Dexter Vines' "Civil War" was going to be a lot different from your typical superhero crossover. The New Warriors had recently been given their own series where they had their own reality series that would follow them on adventures. In 2006's "Civil War" #1, the Warriors were fighting some bad guys when one the villains exploded, killing hundreds of people, including 60 children (it was near a schoolyard). The disaster led to the passing of a Superhuman Registration Act, where superheroes would have to register with the government if they wanted to use powers to fight crime.

Half of the heroes, led by Iron Man, were okay with the new law, while half the other half, led by Captain America, opposed it. Spider-Man, who had recently begun working for Tony Stark, ended up revealing his secret identity as a PR coup for Iron Man's side. Seemingly every issue of "Civil War" changed the Marvel Comics landscape. It was one of the most successful comic book crossovers ever, and it was recently adapted into a hit movie, "Captain America: Civil War").

5 Wolverine: Origin #1

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Marvel was in a strange place in the beginning of the 2000s, as they had only recently gotten out of a bankruptcy and were in a weird state of uncertainty for their future projects (this uncertainty allowed for a lot of experimentation, like Grant Morrison's "New X-Men" and Peter Milligan's "X-Force"). Similarly, comic book sales in general were in a bit of a slump. One way that the company addressed both issues in a big way was with the release in 2001 of "Origin" #1, which detailed the origin story of Wolverine.

Following the success of the 2000 hit film, "X-Men," Marvel believed that if they didn't come up with an official origin for Wolverine, a movie producer was going to do it for them, so they figured that it was better for them to do it themselves. Thus, Bill Jemas, Joe Quesada and Paul Jenkins got together to write Wolverine's origin, revealing his name to be James Howlett and showing his youth growing up in Canada in the late 19th Century. The series was a smash commercial success and one of comics' most famous characters was changed forever.

4 New Avengers #1

Captain America, Iron Man, and the Avengers in a dark storm

"The Avengers" had been one of Marvel's longest-running titles, but outside of a few points here and there (including when Kurt Busiek and George Perez relaunched the title in the late 1990s), the book tended not to have a prominent place in the Marvel Universe. That changed in 2005 when Brian Michael Bendis and David Finch launched "New Avengers," which spun out of the controversial "Avengers Disassembled" storyline from the same creative team, which ended the previous run on "Avengers" with a few members of the team dead and the rest disbanding. The series relaunched with an approach by Bendis of having the most famous Marvel characters all on one team, so Wolverine and Spider-Man both joined the Avengers as full-time members, as did Luke Cage, Spider-Woman and the Sentry.

While a vocal contingent of fans were outraged at how the team had changed, "New Avengers" was a smash hit and Bendis' "Avengers" comics were the centerpiece of the next five major Marvel crossovers, "House of M," "Civil War," "Secret Invasion," "Siege," "Avengers vs. X-Men." Meanwhile, the Avengers became film stars and they were solidified as Marvel's #1 team, a position that would have seemed like a shock had you proposed it in 2001.

3 Identity Crisis #1

The Justice League stand tall in Identity Crisis

Before launching the "Identity Crisis" mini-series event in 2004, writer Brad Meltzer described the project (which was drawn by Rags Morales and Michael Bair) as a love letter to the Silver Age. Whether or not it succeeded in its goal is a matter of dispute, but what is not in dispute is that it was a sales success and that it changed the DC Universe forever.

DC had a bit of a reputation at the turn of the century for being a slightly less violent comic book universe than Marvel's. Heck, in "JLA/Avengers," the DC heroes are even shocked by the Marvel Universe, as it seems so much more violent and depressing than theirs. But notice, of course, that Marvel has been the more successful company for decades now, so there must have been something to Marvel's approach, so "Identity Crisis" was all about following in those footsteps. Murder, rape, betrayal - the series firmly darkened the DC Universe, which only led to more darkening, like the murder of Blue Beetle in "Countdown to Infinite Crisis" or the many violent deaths in "Infinite Crisis". The DC Universe was forever altered, and it all began in "Identity Crisis".

2 Walking Dead #1

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In 2003, Robert Kirkman and Tony Moore launched a new series called "The Walking Dead." Kirkman was so unsure about the success of the book that he only hired Moore for the first six issues and made sure that the first six issues would work as a standalone story if it ended there (there's a reason why there is a major character who dies in that first arc: it's because Kirkman didn't know if they would get a second arc). The book sold pretty well and, with #7, Charles Adlard took over on art duties. Slowly but surely, the book's audience grew and grew and grew until it became a major independent success.

And then "The Walking Dead" TV series debuted. No longer just a successful independent comic book series, "The Walking Dead" was now a phenomena akin to "Batmania" in the 1960s. "The Walking Dead" soon became the #1 watched series on television, getting ratings that television literally hadn't seen since "Friends" went off the air 12 years ago. Kirkman still manages to produce the original comic book series, though, even as the TV series has committed to another two seasons (making you wonder how long the comic can stay ahead of the TV series' plot).

1 Ultimate Spider-Man #1

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In 2000, when "Ultimate Spider-Man" #1 came out, the editor-in-chief of Marvel Comics was still Bob Harras. That's how long ago the Ultimate Universe began. The idea for the Ultimate Universe at first was that it would tell brand-new stories in a new universe free of the continuity restraints of the Marvel Universe. Brian Michael Bendis, Mark Bagley and Art Thibert would re-tell the origin of Peter Parker, the Amazing Spider-Man, but now instead of it all being down in 12 pages, it took six issues to get it all in there.

"Ultimate Spider-Man" was a hit and it was very soon followed by "Ultimate X-Men" and then "Ultimates." The success of "Ultimate Spider-Man" had the effect of making Brian Michael Bendis a very important part of Marvel Comics for the rest of the decade (and then some), but perhaps more importantly, Marvel eventually began to use the "Ultimate" approach on their classic comics, and these changes (particularly to the Avengers characters who appeared in "Ultimates") served as major influences on the Marvel Cinematic Universe, which is the most successful film franchise of all time.

What do you think was the most important #1 issue of the 2000s? Let us know in the comments section!