The "Guardians of the Galaxy Vol.2" trailer has debuted and among the many awesome things shown is the first appearance of Mantis, who will be making her live action debut in the film. Like most of the stars of the first "Guardians of the Galaxy" film before the movie came out, not a whole lot of people know who Mantis is, so let's give you the lowdown on Mantis' comic book history!
Mantis debuted in 1973's "Avengers" #112 by Steve Englehart, Don Heck and Frank Bolle. In the issue, Mantis only appears in a brief aside, where she is talking to some mysterious stranger. Note that right away, Englehart established Mantis' particular way of talking where she would refer to herself in the third person.
The mysterious stranger was revealed to be the Sworsdman in Mantis' first full appearance in "Avengers" #114 (by Englehart, Bob Brown and Mike Esposito).
Despite the ominous cover, the Swordsman and Mantis arrive at Avengers Mansion as good guys. Swordsman, the former villain and brief Avenger (he had joined the team as an undercover agent of the evil Mandarin, but ultimately double-crossed the Mandarin. He still had to leave the team, but when all of the members of the Avengers got back together in "Avengers" #100, Swordsman was allowed to help out), had fallen into a well of deep despair before he met Mantis. He now wanted to redeem himself and become a hero again. The Avengers reluctantly decided to trust him and let him join. Mantis had shown off her great martial artistry skills earlier in the issue in saving the Scarlet Witch from an anti-mutant bigot, but she was not yet looking to join the team herself. She adorably gave all of the Avengers kisses when they let the Swordsman into the group.
Later in the issue, she proved just how strong of an ally she was when she discovered that the malevolent force known as the Lion God was hovering over Avengers Mansion. She discovered this due to her power of empathy, where she can sense the emotions of people around her. She couldn't help but be struck by the sheer anger exuding from the Lion God. She called to it and pretended to be its servant. As part of her plan, she and the Swordsman had to attack the Avengers for real, and Mantis actually took out Thor with just an attack on his nerve clusters!!
Once they showed that it was all part of their ploy to defeat the Lion God, the Avengers were even more sure of their decision to add them to their group. Swordsman and Mantis fought alongside the Avengers for a number of issues, using her martial artistry, her empathy and also some precognitive abilities. Along the way, they learned that Mantis was actually the daughter of a Vietnamese woman and the old Avenger villain, Gustav Brandt, also known as Libra, from the villainous group the Zodiac. After her mother was killed, Brandt left Mantis with the Priests of Pama, a pacifist group of Kree who had a temple in Vietnam. After training her her whole life, they wiped her mind when she became an adult so that she could experience life without any of their interference. She ended up becoming a prostitute and waitress before meeting the Swordsman. It is interesting to note that when Mantis was introduced, there were very few Asian heroes at either DC or Marvel, so she really stood out at the time. Englehart has generally been a writer who will try to create diverse characters when given the chance (his Ultraverse series, "The Strangers", was one of the most diverse superhero groups of the whole 1990s), which is always appreciated (although perhaps one of the first Vietnamese heroines didn't need to also be a prostitute, but hey, baby steps).
While Mantis joined up with the Avengers to be near the Swordsman, she soon found herself drawn instead to Vision of the Avengers, despite the fact that the Vision was dating the Scarlet Witch. Her interest in the Vision clearly emotionally devasted the Swordsman, as seen here in "Avengers" #122 (by Englehart, Brown and Esposito), which was also an example of how Mantis would also refer to herself as "this one" as well as "Mantis".
It's one of the oddest speech affectations of any superhero around.
The Mantis' story in the Avengers took a dramatic change when she learned that she was one of three women (her teammate, Scarlet Witch, was another, as was the witch Agatha Harkness) who might be destined to become the Celestial Madonna, the mother of a powerful cosmic being. Her mate would be the most powerful man in the world, so Kang showed up in the present to make sure that he became that mate (poor record keeping had left Kang uncertain of who precisely the Celestial Madonna was). Her possible destiny as the Celestial Madonna is why her father left her with the Priests of Pama in the first place. Kang made the declaration in "Avengers" #129 (by Englehart, Sal Buscema and Joe Staton)...
Now, you might be thinking, "Um, Kang, two of the three women are young women and one of them is an old lady. You can probably rule Agatha Harkness out" but hey, who knows how celestial birth-giving works? Gotta cover all the bases! Along the way, Kang killed the Swordsman. When the Swordsman died, Mantis realized that she truly did love him. It ultimately turned out that Mantis was the Celestial Madonna, so she married one of the plant creatures known as the Cotati, who re-animated the Swordsman's body, in "Giant-Size Avengers" #4 (by Steve Englehart, Don Heck and John Tartaglione).
She then left Earth with her new weird husband to go mate and give birth to the cosmic baby. Englehart left Marvel not long after Mantis left the Avengers. That's when things got really weird (yes, weirder than marrying a plant alien who re-animated the body of your dead boyfriend), as Englehart then brought Mantis with him to "Justice League of America", as she showed up as a character called Willow in "Justice League of America" #142 (by Steve Englehart, Dick Dillin and Frank McLaughlin). She even still talked in the third person!
Then, in his creator-owned series for Eclipse, "Scorpio Rose", she also appeared in "Scorpio Rose" #2 (by Steve Englehart, Marshall Rogers and Tom Palmer), now calling herself Lorelei (and having given birth to her son)...
When Englehart returned to Marvel in the late 1980s, he brought Mantis with him. She showed up again in "Silver Surfer" #4 (by Steve Englehart, Marshall Rogers and Joe Rubinstein), having given up her child to keep her child protected and having turned green as part of a connection with the Cotati so that she could survive in outer space.
During his "Silver Surfer" run, Mantis was seemingly destroyed but then popped up on Earth towards the end of Englehart's "West Coast Avengers" run back in her human form. Englehart was teasing a storyline where Mantis was split into different aspects of her being. That storyline never came about. Instead, Englehart wrote her out in the pages of his "Fantastic Four" run, specifically in "Fantastic Four" #325 (by Steve Englehart, Rich Buckler and Romeo Tanghal), where she left the world behind to merge with the Cotati and her son.
She next popped up in the controversial "Avengers" crossover, "The Crossing", where she was now married to Kang and was a villain. She showed up in "Avengers" #392 (by Bob Harras, Terry Kavanagh, MC Wyman and Tom Palmer).
This was later retconned to not be Mantis at all, but rather a Space Phantom acting out some sort of strange plot all designed to keep the Avengers from expanding beyond Earth, because if they did, it would eventually lead to humanity taking over the universe.
It was Steve Englehart, once again, who brought Mantis back in the maxi-series "Avengers: Celestial Quest", along with artists Jorge Santamaria and Scott Hanna, where the Avengers teamed up with Mantis (back into her green form) to go visit her son.
She was brought back to the Marvel Universe by Keith Giffen in the now historic "Annihilation Conquest: Starlord" mini-series (with art by Timothy Green III and Victor Olazaba), which famously first put Star-Lord, Rocket Raccoon and Groot on the same team together, as she was part of his team that the Kree put together for a suicide mission.
She then became part of the Guardians of the Galaxy in "Guardians of the Galaxy" #1 (by Dan Abnett, Andy Lanning, Paul Pelletier and Rick Magyar), where her mental abilities saw her serve as the team's therapist.
What she didn't let the team know at the time was that Star-Lord had made her use her mental powers to subtly suggest to each member to join the Guardians. They were not fans of that information. Mantis was seemingly killed at one point, but she turned out to be alive later on.
She was last seen early in the most recent incarnation of the Guardians of the Galaxy (in 2013's "Guardians of the Galaxy" #5, by Brian Michael Bendis, Sara Pichelli and Justin Ponsor), where she helped Star-Lord deal with some "Time Quake" side effects from the then-recent "Age of Ultron" event (which led to Angela becoming part of the Marvel Universe).
She's been in character limbo since then, but it is likely that she'll return to the Marvel Universe right around the time that "Guardians of the Galaxy Vol.2" comes out. It'd be interesting if Steve Englehart was once again the writer who brought her back.