Short answers, pulled from the story.
Karen Gillan plays Nebula in the Marvel Cinematic Universe. She portrayed the character across six films, beginning with Guardians of the Galaxy in 2014, with Guardians of the Galaxy Vol. 3 in 2023 as her final appearance.
Roger Stern and John Buscema created the comic book version of Nebula. She first appeared in The Avengers #257 in July 1985.
Nebula begins the MCU as the secondary villain of Guardians of the Galaxy and gradually becomes an antihero, then a full protagonist. She reconciles with her adoptive sister Gamora, joins the Avengers to help defeat Thanos, and ultimately becomes the leader of Knowhere.
At the end of Guardians of the Galaxy Vol. 3, Nebula remains on Knowhere as the leader of the city, alongside Drax, caring for children the Guardians rescued from the High Evolutionary. Guardians of the Galaxy Vol. 3, released in 2023, was Karen Gillan's final appearance as the character.
The MCU's Nebula is portrayed as Thanos's adoptive daughter and Gamora's adoptive sister, relationships that do not exist in the original comics. In the comics, she claims to be Thanos's granddaughter, is depicted almost exclusively as a villain, and initially appears as an organic humanoid with curled hair. A 2020 comics miniseries later revised her appearance to match the MCU's bald cyborg interpretation.
Karen Gillan was nominated for the Saturn Award for Best Supporting Actress in 2019 for her performance in Avengers: Endgame. She was also nominated for Best Female Newcomer at the 2015 Empire Awards for Guardians of the Galaxy.