One of the ways that The Suicide Squad improved upon its predecessor was how it lived up to its title. What at first appears to be the movie's primary black ops team stumbling into a bloodbath is actually a distraction for Task Force X director Amanda Waller's main squad. That carnage is faithful to the classic Suicide Squad comics by John Ostrander, Kim Yale and Luke McDonnell.
On the flip side, characters inexplicably surviving the team's deadly missions is also part of the source material's appeal. While Harley Quinn is the most obvious example of this trope, another character stands out in that field. Weasel's apparent death is revealed to be a fake-out in a post-credits scene. While Weasel's fate is reminiscent of the comics, his look and backstory are not.
The Suicide Squad's Weasel is animalistic, to the point where his teammates believe he's a werewolf. Despite that, he isn't feral, but more pitiful than anything else. He never speaks. Instead, he's introduced shrieking while exiting the team's transport. His last "line" in the movie is a scream as he's tossed out of a plane and into the sea.
Weasel's apparent death, which causes Rick Flag to realize no one checked to see if he could swim, cements him as a sympathetic character. That and his shabby appearance, complete with bug eyes, make him oddly endearing. That's undercut by the fact that he's in prison for murdering 27 children. The fact that we never see him perform any kind of violence mitigates that somewhat.
By contrast, the original Weasel in the comics was both more human and more murderous than the cinematic version was. Introduced in Gerry Conway, Rafael Kayanan and Ian Akin's The Fury of Firestorm #38, John Monroe was an academic turned serial killer. He took the name Weasel as a reference to one of the insults he received in college.
Monroe used perceived threats to his ability to gain tenure as a college professor as a justification for murdering old classmates. Monroe didn't have any powers. His animalistic looks came from a costume, which included sharp claws. He was also agile and proficient in hand-to-hand combat. While that allowed him to prey on other academics, he was no match for an elemental like Firestorm.
Like many other Firestorm villains, Weasel's run-in with the Nuclear Man led to incarceration and membership in the Suicide Squad. A mission to rescue the superhero Hawk, in The Doom Patrol and Suicide Squad Special by John Ostrander, Paul Kupperberg and Erik Larsen, proved to be even bloodier than Weasel's cinematic outing. Flag is the only survivor of this Suicide Squad mission, partly due to how dysfunctional the team was.
Due to an uncontrolled bloodlust, Weasel murdered his teammate, The Thinker. Thinker would get the last laugh on his killer when Flag donned his helmet in the heat of battle. Thinker's influence caused Flag to murder Weasel. Unlike in The Suicide Squad, this wasn't a fake-out. He did return as an undead Black Lantern in the Blackest Night crossover, albeit as an extra.
Like most DC characters, Weasel was part of the New 52 reboot. Although he was given a more imposing design, Weasel wasn't any more impressive in the new DC Universe. He was quickly dispatched by Killer Frost in Forever Evil: Argus #5, by Sterling Gates and Neil Edwards. Adding insult to injury, Frost not only called him a joke compared to other Firestorm villains but took pity on Weasel.
Neither incarnation of Weasel is an iconic DC villain, but that's another way Gunn's Squad is true to the comics. Icons like Harley Quinn being in the Squad are an exception. It's mainly composed of obscure, expendable villains. It makes the survivors, even the bizarre ones like Weasel, stand out. Gunn has teased that we haven't seen the last of Weasel in his DC Extended Universe work, giving Gunn a chance to work the same kind of magic with Weasel that he did with the similarly obscure Guardians of the Galaxy. It wouldn't be surprising if Weasel joins Groot and King Shark as monsters that Gunn has humanized.