Squirrel Girl is a superhero created by Will Murray and Steve Ditko for Marvel Comics. She first appeared in the comic Marvel Super-Heroes #8, in 1991. Her real name is Doreen Green.

Doreen Green was born in New York City, and spent most of her childhood appearing as a normal girl. However, she had been born with a squirrel tail, and her parents helped her hide it from everyone else to ensure a normal upbringing. At age 10, Doreen discovered she could talk to squirrels, after rescuing a squirrel from a viscious dog. She named him Monkey Joe, and was convinced to use her powers for good. Donning a squirrel-themed costume, Doreen adopted the name Squirrel Girl.

Squirrel Girl's first comic appearance saw her meeting Iron Man, and auditioning to be his sidekick. After Doctor Doom captures them, she uses her swarm of squirrels to chew through the wiring of Doom's ship and defeats him.

Despite being born with her abilities, Squirrel Girl is classified as a "human-mutate" rather than a mutant, due to not being born with the X-Gene. She was originally a mutant in his first appearance but it was changed as to allow Marvel Comics to use her in films or TV shows, instead of 20th Century Fox, who has a legal claim over all mutant characters.

Squirrel Girl posesses all of the proportionate abilities of a squirrel, similar to how Spider-Man has those of a spider. She has superhuman strength, agility, senses, retractable knuckle claws, enhanced jaw strength, and her signature tail which can be used for balance, or as a weapon.

Squirrel Girl has made numerous appearances in various other media. Her first non-comic appearance was in Fantastic Four: World's Greatest Heroes, where she was auditioning for the team. She would go on to appear in shows like Ultimate Spider-Man and games such as Marvel Super Heroes Online, Lego Marvel Super Heroes, Marvel Future Fight, and Marvel Rivals.