Gwenpool (Gwendolyn "Gwen" Poole; colloquial: "GwenPool") is a fictional character appearing in American comic books published by Marvel Comics. A girl from the real world transported to the Marvel Universe, Marvel initially produced two stories featuring Gwenpool as a character, created by Christopher Hastings, Heather Antos and Jordan D. White: first appearing as a backup story in Howard the Duck, and a one-shot Gwenpool Holiday Special, illustrated by Gurihiru. Following the publication of the one-shot, an ongoing series titled The Unbelievable Gwenpool by the same creative team was announced, primarily illustrated by Gurihiru (with Irene Strychalski), which started in April 2016 and concluded in April 2018. The Unbelievable Gwenpool #0, collecting Gwen's appearances from Howard the Duck and the first Gwenpool Holiday Special, was later released, as well as the limited series Gwenpool Strikes Back, Aromancing of Gwendolyn Poole, the final volume of Spider-Man/Deadpool, and Gwenpool (2025). In West Coast Avengers, Gwen is depicted as the owner/mother of Jeff the Land Shark, appearing alongside him in the spin-off series It's Jeff! from its second season onwards. The nemesis of the supervillain MODOK, Gwen faces off against him in The Unbelievable Gwenpool, West Coast Avengers, and MODOK: Head Games.

The story arc Beyond the Fourth Wall introduces an evil future version of Gwen as the archenemy of Miles Morales, later featured as the main antagonist of the video game Marvel Duel, of which Gwen also serves as the protagonist, and as a playable character in Marvel Contest of Champions, Lego Marvel Super Heroes 2, and Fortnite.

In June 2015, following the popularity of Spider-Gwen, all Marvel titles being published had alternate covers with Gwen Stacy reimagined as other characters, such as Doctor Strange, Groot and Wolverine. One of those was Wade Wilson, featured on Chris Bachalo's variant cover for Deadpool's Secret Secret Wars #2. After seeing how many fans were cosplaying as a character who was not even featured in any comic, Marvel editor Jordan White approached writer Christopher Hastings and editor Heather Antos with the task of creating a story around her, with the stipulation of the character being wholly unrelated in backstory to either Deadpool or Gwen (keeping her film and television rights at Marvel Studios, instead of at 20th Century Fox or Sony Pictures). They would introduce the character with a three-issue backup story in the ongoing volume of Howard the Duck (November 2015–January 2016), titled "Ms. Poole if You're Nasty", and then a one-shot comic Gwenpool Special #1 (December 2015). After a meeting with White and Howard the Duck editor Will Moss, Hastings came out with the idea of a character aware of the fourth wall, "but it comes from this place of knowing she is in a comic book because she is from a world where the comic books actually exist", which would also initially lead to a cavalier attitude towards the world in which she inhabits "because she doesn't believe there [are] any consequences to her actions", something Hastings summed as "she decides to [initially] use that [comic book] knowledge like she's in Grand Theft Auto or something". A contrast would be that Gwenpool lacked any of the training or superpowers expected of Marvel characters.

The Howard the Duck arc, from November 2015 to January 2016, was drawn by Brazilian artist Danilo Beyruth, and the holiday special, published in December 2015, had art by Japanese duo Gurihiru. Once Marvel decided to make a Gwenpool ongoing series (named The Unbelievable Gwenpool), starting in April 2016, Hastings asked for Gurihiru's return to the artwork team, with the title being edited by Antos, The Unbelievable Gwenpool solo series ended at issue #25. also appearing in the specials Gwenpool Holiday Special: Merry Mix-Up #1 and Edge of Venomverse #2. Gwenpool then joined the Fresh Start incarnation of the West Coast Avengers in 2018. After that book ended, the character starred in the 2019 limited series Gwenpool Strikes Back, written by Leah Williams and drawn by Spanish artist David Baldeón, and appeared in the 2020–21 promotional limited series MODOK: Head Games by M.O.D.O.K. showrunners Patton Oswalt and Jordan Blum (with art by Scott Hepburn) as a supporting character. In 2022, she was added as a main character to the webtoon series It's Jeff!, written by Thompson and illustrated by Gurihiru, raising her "son" Jeff the Land Shark along with Kate Bishop. In 2023, Gwen starred in a five-issue storyline in the romance anthology series Love Unlimited entitled "Aromancing of Gwendolyn Poole" ("A Romancing of Gwendolyn Poole"), written by Jeremy Whitley, in which the citogenesis-induced interpretation of the character being aro-ace was made canon in the text. The same year, she appears in Alligator Loki attending a beach day with Jeff and Laura Kinney, illustrated with red hair and a blue beachwear version of her suit due to the series' colorist Pete Pantazis (on not being given a reference image for "Gwen" and not being familiar with Gwen Poole's character) having decided to instead give her the red hair and blue color scheme of Gwen Tennyson from Ben 10 as an Easter egg. As part of the 2024 Venom War event, Gwen was featured in the one-shot Venom War: It's Jeff #1 (November 2024), again written by Thompson and illustrated by Gurihiru. In May 2025, Gwen returned in the solo series The All-New All-Deadly Gwenpool (or simply Gwenpool), following her as she and Kate team up with Peter Parker against a purple-clad impostor Gwenpool: Gwen Stacy, resurrected with Weapon X-like abilities as the hyper-violent X-31. After being rendered a ghost, Gwen then possesses Peter to face X-31 before being returned to life.

Gwendolyn "Gwen" Poole arrived to the Marvel Universe from what she claims to be "the real world". In her home reality, Gwen had been a comics superfan as an escape from her life as an unemployed 18- (or 19-)year-old high school dropout. Unwilling to be an "extra" in the Marvel world, she went to a tailor for superheroes and requested her own costume. The tailor (named Ronnie) complied, but misread Gwen's application form, and thought Gwen went by the alias of "Gwenpool", leading to a costume similar to Deadpool's. Upon gaining the ability to manipulate the borders of the fourth wall from an attempt to return her to reality, allowing her to travel in time, Gwen retcons the Marvel Universe into believing her to be a mutant after being given the idea by Kamala Khan, allowing her to enter the gates of Krakoa.

Gwenpool's first appearance as a character was in Howard the Duck Vol 6 #1 (later republished in The Unbelievable Gwenpool #0), when she was involved in stealing a humanity-destroying virus from Black Cat and selling it to Hydra to get money easily, believing that the Avengers would simply deal with any consequences. When she revealed to Howard the Duck the item she had stolen from Hardy and to whom she had sold it, Howard scolded her and informed her that the Avengers were not available to save the Earth from the virus. Guilt stricken, she then set out with Howard to retrieve the virus from a Hydra base.

In the 2015 Gwenpool Special, Gwenpool is hired on her first mercenary job, to kill a villain. After completing her mission, Gwenpool attends a Christmas party hosted by She-Hulk, where she is seen talking to Ms. Marvel.

Following the events of Gwenpool Holiday Special #1, Gwenpool becomes a full-time mercenary. While trying to deposit the money she made killing Orto, Gwen stops a bank robbery by killing all of the robbers, except for the gang's hacker Cecil, whom she enlists as a reluctant sidekick. After a mission revolving around extraterrestrial arms dealers where she killed MODOK Superior's best agent and took credit for his work, MODOK tracked Gwenpool down. He murdered Cecil to persuade her to become his henchman and an agent for his Mercenary Organization Dedicated Only to Killing. Gwenpool joins MODOK's elite squad, which also includes the alchemist Mega Tony, the magician Terrible Eye, and Batroc the Leaper, who gives Gwen basic combat and firearms training.