Doreen Allene Green was born to Dorian and Maureen Green in Canada. When she was 10 years old, Doreen discovered she could communicate with squirrels; she suffered a modification in her genes for unknown reasons that granted her squirrel-like abilities, which manifested predominantly as a prehensile tail. When her parents consulted a doctor, it was determined that Doreen was not a mutant, even though she believed so for a long time. She is first seen as Squirrel Girl ambushing
Iron Man in a forest, hoping to impress the veteran hero and become his
sidekick. The 14-year-old introduces herself and her pet squirrel Monkey Joe and displays her squirrel-themed abilities. After she rescues Iron Man from
Doctor Doom with the help of a horde of squirrels, Iron Man says she is too young to fight crime, but that he will put in a good word for her to the Avengers when she is older. Years later, having moved to
New York City, Doreen joins the
Great Lakes Avengers. Squirrel Girl introduces each issue of the team's miniseries, providing an opinion about the contents of the series. Her sidekick Monkey Joe also joins the team and comments upon the series as well. He is later killed by
Leather Boy, a rejected GLA member who was disguised as Doctor Doom. Enraged by the death of her friend, Squirrel Girl demonstrates the true extent of her powers when she defeats the villain
Maelstrom by overwhelming him with a literal army of squirrels. She finds a new squirrel companion during this battle, the only one of her squirrel army who survived. Doreen names her
Tippy-Toe. After receiving a subpoena from the
Avengers and discovering that her teammates are all mutants, the team renames themselves the "Great Lakes X-Men", complete with new costumes. During the
GLX-Mas Special, Squirrel Girl and Tippy-Toe single-handedly defeat the
supervillains
MODOK,
Terrax, and
Thanos.
S.H.I.E.L.D. agent
Dum Dum Dugan tries to recruit her, explaining that the organization had been watching her for some time. Doreen declines the offer, saying she is happy with the Great Lakes X-Men. After helping the
Thing defeat
Bi-Beast, Squirrel Girl was invited to the annual Superheroes
Poker Tournament and brought the team with her. In the end,
Flatman won the tournament with a straight flush, beating the Thing's four fours. After being discouraged from using the names X-Men and
Defenders by members of those teams present at the tournament, and since Flatman was the champion of the tournament, the team renamed themselves the Great Lakes Champions, despite protests from former
Champions of Los Angeles member
Hercules. During the
Civil War crossover storyline, Squirrel Girl and the Great Lakes Champions registered under the
Superhuman Registration Act, as revealed when
Deadpool attempted to apprehend them for violating the Act, only to be defeated and informed that they had already registered. Under the Registration Act, Squirrel Girl remains a member of the again-renamed Great Lakes Initiative. Squirrel Girl and the GLI, along with Deadpool, are sent to save
Dionysus after he fell from
Mount Olympus and was captured by
A.I.M., who planned to use his powers to cause mental instability in superheroes they consider a threat. After their victory, Squirrel Girl helps Dionysus back to Olympus and to his own bed to sleep it off. It is later revealed that she is a fan of the superhero team the
New Warriors, especially
Robbie Baldwin, the hero Speedball, on whom she has a crush, and the two eventually share a kiss. They later appeared to welcome Gravity as leader of the team, after he was transferred to Wisconsin by
Norman Osborn. After defeating
Fin Fang Foom and finding little support from her teammates on the again renamed Great Lakes Avengers, whom she believes have her shoulder most of their work, she exits the group. When
Luke Cage and
Jessica Jones seek a nanny for their daughter
Danielle Cage, they hire Squirrel Girl. It is also revealed that Doreen had a brief relationship with
Wolverine (then a member of the New Avengers), which did not end happily. and he leaves the Earth to live another day. When she arrives back home, her roommate Nancy Whitehead tells her that she has figured out she is a superhero, but promises not to tell anyone, the two becoming good friends. Later, Squirrel Girl and other superheroes defeat
Mysterion, who was attacking
Liberty Island with an army of robot dinosaurs. Shortly thereafter, while attempting to stop
Hippo from robbing a bank, she meets
Chipmunk Hunk and
Koi Boi, both of whom have the ability to speak to different animals. Nancy reveals their secret identities (Tomas Lara-Perez and Ken Shiga, respectively) to her, since she easily recognized them under their masks. They later encounter a monstrous Asgardian squirrel god,
Ratatoskr, who had been causing mayhem on the city by trash-talking its citizens during their sleep, but is defeated with help from
Loki and the
current and former
Thor. During their second college year, Doreen and Nancy encounter
Brain Drain and quickly defeat him due to his outdated technology and crucial design flaws. Upon realizing that he did not have a choice about his evil actions due to his programming, Doreen and Nancy update his technology to modern standards. When he awakens, Brain Drain reveals that he intended to reform and ends up enrolling at ESU to take computer science courses. Later, she and her classmates get sent back in time to the 1960s by fellow student Cody, who sent them away from the present time to curve his grade. Nancy, the only person who remembers Doreen's existence, goes back to rescue her along with a past version of Doctor Doom, who then learns that he will successfully take over the world thanks to a copy of Wikipedia on Nancy's phone. In the present day, Cody wakes up to a Doctor Doom dystopia and takes himself back to the 1960s with an older, future Doreen to help fight Doom. Doreen defeats Doom by repeatedly using Cody's time machine to send herself a day before the fight, creating a small army of Squirrel Girls that swarm Doom and force him to give up. Doreen and the students are sent back to the present, while future Doreen stays behind and continues to foil Doom's schemes. Later, she gets jealous when her crush Chipmunk Hunk, starts dating a classmate named Mary. Nancy, Tippy-Toe, and Koi Boi help set her up an online dating profile, which leads to many unsuccessful dates, one of which ends with an encounter with the
Mole Man, who is angered by how Doreen's earlier suggestions to Kraven has affected his home. Doreen apologizes to him and the two have a conversation about his situation, leading the Mole Man to proposing to Doreen on the spot and several subsequent schemes to get Doreen to go on a date with him. He threatens to bury a number of worldwide landmarks if she does not date him, and after Nancy is nearly kidnapped by him and being swarmed by the media, she goes to confront Mole Man only to find that
Tricephalous is in love with him. Doreen lets the beast defeat her to woo Mole Man and get him off her back for good, and decides that dating is not right for her at the moment after seeing that Mary is a nice fit for Chipmunk Hunk. Squirrel Girl also had an alternate version of herself due to time travel running around for decades interfering with Doctor Doom's plans. As a result, she released an A.I.
Doombot that eventually becomes
Gwenpool's nemesis, Vincent Doonan. They later reconcile and at Gwen's insistence he even lets Squirrel Girl examine him for her computer class. She then follows Gwenpool to Hell to rescue her brother Teddy Poole and they defeat
Mephisto. While there though Gwen points out that in the Marvel universe the devil is very real and punchable, suggesting that heroes should do so all the time confusing Squirrel Girl. Running out of pages, Gwen then leaves, getting Teddy back to Earth to her and runs off to do other things before her comic comes to an end. Another alternate version of Squirrel Girl is created when Doreen falls into a piece of technology which Tony Stark had obtained from the
High Evolutionary; the clone is nicknamed Allene and is like Doreen in most every way except she is lacking in the restraint and empathy which largely defines Doreen's career as a superhero. Allene strives to create a world where squirrels are the dominant species, sending an army of squirrels into the cloning device to rid them of their restraint and imprisoning every superhero who stands in her way in the
Negative Zone. When Doreen gives her last effort to appeal to Allene's humanity, Allene instead banishes Doreen to the moon, where a dying Doreen summons
Thor's hammer
Mjolnir, becoming
Squirrel Thor. Squirrel Girl later becomes a member of the
U.S.Avengers. She later receives a wealthy benefactor in Melissa Morbeck, a woman who can talk to animals who gives Doreen a new "flying squirrel" suit. Morbeck is quickly revealed to be a supervillain, however, who uses technology to exert sadistic control over animals and unleashes an army of insects and wild animals on the city, disguising one of her animal minions as
Doctor Doom. While Squirrel Girl, Chipmunk Hunk, and Koi Boi subdue the animal army, Nancy and Mary set off an electromagnetic pulse to disable Morbeck's control over the animals, leading to her arrest. Later stories see Squirrel Girl traveling to the
Savage Land and outer space, where she clashes with
Loki,
Drax the Destroyer, and the
Silver Surfer. After she returns home, a clash with a small-time livestreaming criminal inadvertently sends Doreen and Nancy into hypertime; the two girls quickly age into elderly women and become close as they find common interests. They eventually devise a means of reversing time, so they revert to teenagers and forget their lives together, but Doreen finds a note written by her future self to preserve the memory of the happiness they shared. While visiting Allene in the Negative Zone, Squirrel Girl is summoned by Loki to help fight the
Frost Giants in the
War of the Realms. There she once again encounters Ratatoskr, with whom she clashes yet eventually forms an unlikely, if uneasy, alliance. Afterwards, Melissa Morbeck returns with an alliance of supervillains (including Doctor Doom,
MODOK Superior,
Leader, and
Whiplash) to enact revenge on Squirrel Girl – kidnapping Brain Drain, stealing Iron Man's armor, attacking Doreen's apartment, and finally publicly leaking her
secret identity. Several heroes and villains from across the
Marvel universe come to Squirrel Girl's aid, including
Kraven the Hunter, Ratatoskr,
Rhino,
Mole Man, Tony Stark, and eventually
Galactus, who uses the Power Cosmic to teleport away Morbeck and her allies and return Stark his armor. Afterwards, Stark publicly broadcasts a video which celebrates Squirrel Girl's various achievements. In the aftermath of the attack on her apartment and her leaked secret identity, Squirrel Girl briefly retires from active heroism and instead starts hosting an
AM broadcast call-in show called "The Unbeatable Squirrel Girl Radio Show", where she answers questions regarding what it's like to be a superhero. She's joined by her friends Tippy-Toe, Nancy Whitehead, Koi Boi, Chipmunk Hunk, and Brain Drain. ==Powers and abilities==