Susan Alexandra Weaver (born October 8, 1949), known professionally as Sigourney Weaver (), is an American actress. Following her film debut as a minor character in Annie Hall (1977), she quickly came to prominence with her first lead role as Ellen Ripley in Alien (1979). She reprised the role in three sequels: Aliens (1986), for which she was nominated for the Academy Award for Best Actress; Alien 3 (1992), and Alien Resurrection (1997). She is also known for her starring roles in the box-office hits Ghostbusters (1984), Ghostbusters II (1989), and Avatar (2009).

Weaver was nominated for a Drama Desk Award for the 1980 Off-Broadway play Das Lusitania Songspiel, and received a Tony Award nomination for the 1984 Broadway play Hurlyburly. A seven-time Golden Globe Award nominee, she won both Best Actress in Drama and Best Supporting Actress for her work in the films Gorillas in the Mist and Working Girl (both in 1988), becoming the first person to win two acting Golden Globes in the same year. She also received Academy Award nominations for both films.

For her role in the film The Ice Storm (1997), she won the BAFTA Award for Best Actress in a Supporting Role. Additionally, she has received three Emmy Award nominations and won two Saturn Awards.

Weaver acquired the nickname of "the Sci-Fi Queen" for her numerous contributions to science-fiction film history. Other popular works she has appeared in include Galaxy Quest (1999), Futurama (2002), WALL-E (2008), Paul (2011), The Cabin in the Woods (2012), Finding Dory, and A Monster Calls (both in 2016). She returned to Broadway in 2013 to star in Vanya and Sonia and Masha and Spike. Weaver played Alexandra Reid, the main antagonist, in The Defenders which premiered on August 18, 2017.