The MCU has been well-known for packing in as many Marvel Comics easter eggs and superheroes as possible. From subtle teases like the classic Human Torch to more bombastic hints at Howard the Duck, fans have much to look at with the movies. However, it's not just gratuitous cameos from comic heroes and villains that the MCU has under its belt. Several times, Marvel has been able to bring in celebrities to make an appearance in their films. Whether it's famous actors or people relevant to the history of Marvel Comics, there are all kinds of interesting appearances in all of the Marvel movies. From the very start, directors have been throwing some familiar faces that are so difficult to catch that, if you blink, you'll miss it easily.

Over the years, Marvel has revealed some of their more famous cameos that we've all noticed. However, because the MCU has been going on for over ten years now, there's a chance that you've forgotten some of  the big actors and celebrities who've been seen hanging out with Marvel's Avengers and Guardians of the Galaxy. Pay attention the next time you watch a Marvel movie because you won't want to miss these 15 actors you forgot were in the MCU.

15 OLIVIA MUNN IN IRON MAN 2

Olivia Munn, known for her recent work as Psylocke in X-Men: Apocalypse, actually had experience in the superhero genre before appearing alongside the likes of Quicksilver, Professor X, and Phoenix. The ex-G4 host spent her time as a TV host in the film, announcing an event that Tony Stark was heavily involved with.

What made her cameo disappointing to many is that there were rumors floating around that she'd be playing an important Marvel character like Scarlet Witch or the Wasp. She wasn't quite big enough at the time to score such an iconic role, but at least she'd be later given her chance to shine in the action movie department. Would you have liked to see Olivia Munn over Elizabeth Olsen as Scarlet Witch?

14 ALEXIS DENISOF IN THE AVENGERS

The Other Avengers

Joss Whedon was one of the most interesting choices to direct The Avengers, only having a hand in TV projects like Buffy the Vampire Slayer and Angel prior to that. Despite working on a bombastic superhero blockbuster, he didn't waste the opportunity to have a little nods and references to his old shows (which exist in a realm fans call the Whedonverse).

One actor from the aforementioned TV shows that Joss Whedon worked on is Alexis Denisof, who actually appeared in The Avengers. The character he played was the Other, the creepy servant of Thanos. Denisof would later reappear in the MCU for Guardians of the Galaxy. However, his time wouldn't last long, as he would be killed within seconds by the ruthless Ronan the Accuser.

13 ROB ZOMBIE IN GUARDIANS OF THE GALAXY

There are a lot of fascinating cameos in the Guardians of the Galaxy series, but none of them more fascinating than Rob Zombie. The famous musician didn't have an actual physical role in the film. All he had to do for his paycheck was record dialogue and be on his way -- he didn't even sing for James Gunn's space opera.

Fans with the ears of a fox probably caught Zombie's role in the movie. He served as the voice of the massive Ravager ship that Yondu and the rest of his goons lived on. Rob Zombie would continue his cameo tradition in Guardians of the Galaxy Vol 2, where he played a background Ravager that is extremely difficult to spot. It's still shocking that Marvel would be willing to draft musicians for cameos and not have any reference to their singing.

12 LOU FERRIGNO IN THE INCREDIBLE HULK

best-marvel-cameos-lou-ferrigno

After the disaster that was director Ang Lee's 2003 Hulk film starring Eric Bana, Universal wanted to get back on the right track by releasing The Incredible Hulk to coincide with the newly-formed Marvel Cinematic Universe that started in 2008 with Iron Man. The result was another superhero movie that was underwhelming, but it did have its fair share of cameos and references.

One of the more respectable cameos in the movie was by Lou Ferrigno. Older folk might've easily recognized him, but younger people wouldn't remember that he played the Incredible Hulk in the classic live action TV series. Before they had CGI to create the radioactive monster, they had to use actors who were massive and muscular. At the time, Lou Ferrigno was the perfect choice.

11 ELON MUSK IN IRON MAN 2

Elon Musk in Iron Man 2

Brilliant minds in the real world pale in comparison to what Tony Stark is capable of, but that doesn't mean that they aren't relevant to the MCU. Eagle-eyed fans of Iron Man 2 will have noticed a strange appearance by a man in a white jacket. After some light conversation with Pepper, we hear her refer to him as "Mr. Musk."

It's not long after that when Tony interjects, being his usual Stark-y self. He states that he's a big fan of Musk's work, and the rich man then says that he has ideas for electric planes in the future. Stark says that he'll make it work before parading away with his woman at his side. If that's Marvel's way of making literally everything feel "connected," then they've succeeded in a seriously meta way.

10 NATHAN FILLION IN GUARDIANS OF THE GALAXY

MCU Cameos You Totally Missed

Nathan Fillion, made famous for his performances in Firefly and Castle, has had an interesting relationship with the Guardians of the Galaxy franchise. In the first film, he appeared when the Guardians were taken to the Xandarian prison in space. A blue alien walks up to Star-Lord and makes a comment about him being the "new meat."

After that, Rocket and Groot show up to make it known that Star-Lord is their bounty and that anyone who wants to get to him has to go through them. Groot then rips out the alien's nose and drops him to the ground. Little did many people know that Nathan Fillion provided the voice for that character. The actor was also set to appear in Guardians of the Galaxy Vol 2 as Wonder Man.

9 TOM MORELLO IN IRON MAN

Tom Morello in Iron Man

The Ten Rings is a powerful organization that sought to terrorize the world and painful and supernatural ways. Despite how crucial the organization was to the existence of Iron Man in the comics, they seemed to have little relation to how the Mandarin was executed in the MCU. That said, they weren't lacking in some famous soldiers.

In the first movie, Tony Stark finds himself directly at odds with the Ten Rings and has to fight many of their goons off. Among them is the guitarist known as Tom Morello (you may know him as a boss in Guitar Hero 3). The reason Tom was given a cameo in the film was because he played guitar for the soundtrack of the film and later returned to do the same for Iron Man 2.

8 MILEY CYRUS IN GUARDIANS OF THE GALAXY VOL 2

James Gunn has seriously done his homework. In both Guardians of the Galaxy movies, there are so many nods and references to Marvel Comics history. However, he really outdid himself when it came to the second outing with our favorite dysfunctional space team.

Several times in the film, we are given hints of the classic Guardians of the Galaxy team who are Ravagers in the context of the MCU. We get a clear picture of who they all are at the end of the movie, where Sylvester Stallone rallies them once more. One of the aliens who talks is a little robot known as Mainframe. When it starts talking, some of the old Disney Channel fans might recognize that higher-pitched voice. Of course, the actor behind the character is Miley Cyrus.

7 LUKE HEMSWORTH IN THOR: RAGNAROK

Loki is one for tooting his own horn, and never was that more on display than in Thor: Ragnarok. The film showed him putting on a play of the events of the previous movie, with various Asgardians acting as stand-ins for himself, Thor, and Odin. Some familiar faces were already playing Thor and Loki, but people might not have recognized Thor's actor immediately.

On a closer glance, it's clear that this version of Thor looks strangely similar to the actual Thor. This is because he is played by Luke Hemsworth, the older brother of Chris and Liam Hemsworth. He never became famous in the acting world, but is fairly well-known simply by association. Having him stand-in as the God of Thunder was a nice way of nodding to their familial connection.

6 GARRETT MORRIS IN ANT-MAN

Garrett Morris in Ant-Man

During the Ant-Man movie, Scott Lang is present in numerous battles and weird scenarios. When he first puts on the suit and shrinks down, he gets wound up in all sorts of trouble. Eventually, he gets thrown out of the building and lands on top of a car, denting the roof. The camera then goes to a shot of the man looking up in confusion.

Most people won't know who this is, but serious comedy fans will recognize him as Garrett Morris, a comedian who appeared during the early days of Saturday Night Live. He was involved in a sketch where various other superheroes were present. He played Ant-Man and was made fun of because nobody thought he had any sort of interesting powers to bring to the table.

5 JOAN RIVERS IN IRON MAN 3

When it comes to gratuitous cameos, the Iron Man franchise has been anything subtle (they've even gone as far to liken Stan Lee to Hugh Hefner). During Iron Man 3, there were several newscasts that took place throughout the film. They were set to provide some commentary on events that were happening. When it was revealed that Rhodey was wielding the new Iron Patriot suit over War Machine, we see a bit where Joan Rivers has a few things to say.

She states that it's just the War Machine armor with a fresh coat of paint and that the government was really trying to hit the public over the head with the "America" theme. Her co-host thought the comment was funny and burst into laughter in response. To be fair, it was a bit redundant by that time because Captain America was already awake.

4 JAMES GUNN'S DOG, VON SPEAR IN GUARDIANS OF THE GALAXY

Several times in film, directors will be able to throw in their children or their siblings in for a few shots and call it a day. While James Gunn did use his brother in Guardians of the Galaxy, he managed to use his lovable dog as well. Before you start thinking, no, Von Spear was not the dog used to play Cosmo.

Instead, James Gunn's dog appears at the beginning of the movie. Star-Lord is on a mysterious planet looking for the orb housing an Infinity Stone. He uses a special device to depict the planet when it was thriving and full of people. There's a brief shot of a holographic dog walking across the screen. This was the small appearance by Von Spear. No doubt, only the Gunn family got a kick out of that cameo.

3 KATE MARA IN IRON MAN 2

Tony Stark wasn't exactly on the good side of the government after he announced that he created the Iron Man suit and wouldn't share the technology. This is why the Armed Forces decided they needed to see him in court. However, to notify him, they had to give Tony a subpoena so that he couldn't be absent.

In Iron Man 2, a U.S. marshal came to Stark and gave him the subpoena. This marshal was played by Kate Mara, famous for her work on House of Cards. This wouldn't be the last superhero movie she'd ever appear in, though, as Kate would later play Susan Storm in the universally-hated Fantastic Four reboot by Josh Trank. Despite how awful that movie was, you'll be shocked to hear that she was willing to do a sequel down the road.

2 MATT DAMON IN THOR: RAGNAROK

Matt Damon is known for being in movies like The Martian and the Jason Bourne series. He's a big actor when it comes to both action and drama, so it makes sense that Marvel would knock on his door for a project at some time. However, no one expected his first MCU appearance to be as weird as it was.

In the beginning of Thor: Ragnarok, we see Loki (disguised as Odin) watching some Asgardians act out the events of Thor: The Dark World where Loki looks like the hero. Once we get a close-up of the actor playing Loki, the memory bells start ringing in our heads. Believe it or not, the man wearing that golden reindeer helmet is none other than Matt Damon himself.

1 SETH GREEN IN GUARDIANS OF THE GALAXY

Howard the Duck Guardians of the Galaxy

Seth Green is a man known for his comedic work. His claim to fame came from his role as Chris Griffin in the popular adult comedy, Family Guy. However, he has worked in a lot of movies, both as a voice actor and a real appearance. He had a major role in Buffy the Vampire Slayer and played more to his comedic roots in other projects.

Of course, there was no better choice in James Gunn's mind for a special cameo at the end of Guardians of the Galaxy. After the Collector looks around at his destroyed facility, we get a shot of Howard the Duck cracking a joke at him. This sarcastic duck is played by none other than Seth Green, who would later reprise his role in Guardians of the Galaxy Vol 2.