Katy O'Brian first appeared in the Marvel universe as a minor villain in the final season of Agents of S.H.I.E.L.D. before taking a larger role in Ant-Man and the Wasp: Quantumania. Her early character met a quick end, but the de-canonization of the TV series allowed her return in the films.
Katy O'Brian entered the Marvel Cinematic Universe on television, playing Kimball, a small-time antagonist in season 7 of Agents of S.H.I.E.L.D. This series, which began as a direct spin-off from The Avengers, centered on Agent Phil Coulson—portrayed by Clark Gregg—surviving his apparent death in the 2012 film. Over time, the show diverged into its own timeline through a time travel storyline, separating it from the main MCU continuity. O'Brian's Kimball was part of Nathaniel Malick's crew, played by Thomas E. Sullivan, consisting of characters fated to die in their original timelines. During a confrontation with S.H.I.E.L.D., Kimball and her allies were transported to the Quantum Realm, where Quake, played by Chloe Bennet, destroyed the alien time ship, killing them all. Reflecting on the role, O'Brian told Deadline, 'I came in really late in Agents of S.H.I.E.L.D. I had a really small [part]... I had like two lines and stood in the background for a while, and then I think I blew up or something.' Marvel's decision to de-canonize Agents of S.H.I.E.L.D. enabled O'Brian's return in Ant-Man and the Wasp: Quantumania, where she portrayed Jentorra, the leader of the Freedom Fighters in the Quantum Realm. Jentorra allied with Ant-Man (Paul Rudd), the Wasp (Evangeline Lilly), and Stature (Kathryn Newton) to battle Kang the Conqueror (Jonathan Majors) in the film's climactic fight, ultimately helping defeat him. While O'Brian's Jentorra survived the movie's events, no future appearances have been announced. This casting marks a rare instance of an actor reprising a Marvel role across de-canonized TV and films, following examples like Charlie Cox in Daredevil and Spider-Man: No Way Home, or Teyonah Parris from WandaVision in The Marvels.