Warning: The following contains spoilers from the Hawkeye season finale, now streaming on Disney+.
The Hawkeye season finale was full of surprises, including a reveal about Laura Barton (Linda Cardellini), Hawkeye / Clint Barton's (Jeremy Renner) wife.
A running plotline throughout the series involved Hawkeye chasing down an old watch that was taken from Avengers Tower and auctioned off on the black market. Clint finally got his hands on the timepiece in the season finale, "So This Is Christmas," where it was revealed that it belonged to Laura and that she used to be S.H.I.E.L.D. operative Agent 19. While the series did not provide any other details about Laura's past, Hawkeye director Rhys Thomas said that it could come up again in other Marvel Cinematic Universe (MCU) projects.
"We've seen her over these years as his wife, and there was obviously a desire [to expand her backstory]," Thomas said. "We should know more about her. There's more to her than just staying at home with the kids. It was a fun little thing to tease out over the season and again a nice little payoff that hopefully promises more of a character planted at the end."
Created by writer Len Wein and artist Neal Adams, Agent 19 first appeared in Astonishing Tales #6 back in June 1971 and is the ex-wife of comics Clint Barton / Hawkeye. In the comics, however, her real name is Barbara Morse, and she also goes by the codename Mockingbird.
Adrianne Palicki portrayed Bobbi Morse / Mockingbird in Agents of S.H.I.E.L.D, potentially raising some continuity questions within the MCU. However, Agents of S.H.I.E.L.D's status in the MCU is a bit up in the air, as it is unclear if it is canon, part of a different MCU timeline or completely outside the MCU. Marvel Studios is known for loosely adapting the comics its properties are based on, so it is quite possible that Palicki and Cardellini's characters can each exist on their own in the proper MCU as Bobbi Morse / Mockingbird and Laura Barton / Agent 19, respectively.
Cardellini's Laura first appeared in Avengers: Age of Ultron, where it was revealed that Clint was married with a family. Since then, she has only appeared in one other MCU movie: Avengers: Endgame.
Source: Marvel