Monkey Joe was the squirrel sidekick of Squirrel Girl. He was smarter than an average squirrel, which may have been the reason he was her constant companion even though she could talk to all squirrels. He even showed an affinity for the use of computers.
Monkey Joe helped her to defeat Doctor Doom. Squirrel Girl and Monkey Joe joined the Great Lakes Avengers (GLA) (and Squirrel Girl made certain that Monkey Joe was an official member).
Monkey Joe met his demise seemingly at the hands of Dr. Doom (whom he had helped defeat). This turned out to instead be Leather Boy, an ex-GLA member kicked out for not actually having any powers, who was dressed in a variation of an old Doctor Doom costume.
After his death, Squirrel Girl found a new squirrel companion named Tippy Toe and gave her a pink bow. Tippy Toe mimics Monkey Joe's role as Squirrel Girl's sidekick.
Monkey Joe was seen playing cards with the rest of the fallen GLA members when Doorman briefly visited the after-life. He seemed very bitter about his demise and less forgiving than the other deceased members.
In 2005, Squirrel Girl and Monkey Joe were revived from obscurity for their first ever miniseries written by Dan Slott.
Monkey Joe's death was part of a marketing promise that a member of the GLA would die in each issue of the miniseries, as a parody to comic book deaths.
Monkey Joe also served as a comedic commentator for the GLA miniseries. A cartoony version of him appeared alongside the story holding signs with humorous, often smart-ass, remarks on the events of the story. After his death in issue #3, the narration circle showed a deceased Monkey Joe hanging lifeless. His presence in the narrator circle continued in issue #4, however he now possessed a halo.
The trade paperback of the GLA miniseries is dedicated to the memory of Monkey Joe, and reads "Monkey Joe 1992-2005. He loved nuts. He will be missed."