Squirrel Girl (Doreen Allene Green) is a superheroine appearing in American comic books published by Marvel Comics. Created by writer Will Murray and writer-artist Steve Ditko, the character first appeared in Marvel Super-Heroes vol. 2 #8, a.k.a. Marvel Super-Heroes Winter Special (cover-dated Winter 1991). Murray created the character out of a desire to write lighthearted stories, in contrast to the heavily dramatic tales that were then the norm in mainstream comics.

Although distinct from Marvel's mutants, Doreen has a genetic anomaly which gives her the ability to communicate with squirrels. She has been a member of both the Avengers and the Great Lakes Avengers, and has been a supporting character in stories featuring Luke Cage and Jessica Jones. Doreen has also appeared in her own solo series, The Unbeatable Squirrel Girl, which has depicted her dividing her time between her superhero adventures and her work as a college student.

Squirrel Girl was created by writer Will Murray and artist Steve Ditko, making her debut in "The Coming of ... Squirrel Girl" in Marvel Super-Heroes vol. 2 #8, a.k.a. Marvel Super-Heroes Winter Special (cover-date Winter 1991). She ambushes the superhero Iron Man, teams up with him, and, after Iron Man is captured, defeats the villainous Doctor Doom. The story also introduces her squirrel sidekick, Monkey Joe.

Murray has since described the character's genesis:

Actually I created Squirrel Girl in script form without any artist input. Tom Morgan was originally going to draw it, but when he dropped out, I requested Ditko and got him. Ditko did a great job in bringing my baby to life. He invented that knuckle spike. It wasn't in the script. I based Squirrel Girl ironically enough on a long–ago girlfriend who read comics and was into "critters"—wild animals of all types. Coincidentally, she was a big Ditko fan. I think I got the idea because I had a bunch of squirrels running around my roof and sometimes coming in through my open bedroom window and inspiration struck.

Murray attempted to pitch a follow-up story where Squirrel Girl tried to join the Fantastic Four, but it was turned down. Despite Marvel acknowledging the character's "coolness", Murray was told that she did not feel like a Marvel character and that they most likely would not use her again.

Squirrel Girl next appeared in Marvel Year-In-Review '92, where she made a one-panel appearance in the self-satirizing book's Marvel 2099 section, where "Squirrel Girl: 2099" was listed as one of "the 2099 books we've pretty much ruled out" as actual future titles. Later, she was slated to join the New Warriors, but writer Fabian Nicieza left Marvel before going through with his plan. In 1997, Fleer-Skybox released cards based on Marvel Superheroes, one of which was a more sexualized version of Squirrel Girl.

She did not appear again for nearly a decade. She was mentioned only once in comics during that time: In Deadpool #7, Deadpool's friend/maid/mother-figure/prisoner Blind Al mentions accidentally putting "bleach in with [Deadpool's] Squirrel Girl Underoos."