Summer Glau is an American dancer and actress, known for playing River Tam in the short-lived science fiction series Firefly and follow-up movie Serenity, and for playing Cameron in the series Terminator: The Sarah ConnorChronicles.

Glau was born in San Antonio, Texas, where she grew up with her two younger sisters, Christie and Kaitlin. Glau received a scholarship to a ballet company and was home-schooled from grades 3 to 12 to accommodate her ballet training. After a serious ankle injury finished her dancing career Glau took time off from dancing to visit friends in Los Angeles, where she auditioned for several television commercials. She later moved to Los Angeles to pursue a more active acting career. She is of Scotch-Irish and German descent.

Glau was classically trained as a ballerina and also studied tango and flamenco. A professional dancer since age 12, she appeared in several television commercials. Having relocated to Los Angeles in 2002, Glau's first television credit was a guest role as a ballerina on the 2002 episode "Waiting in the Wings" (episode 3x13) of the television series Angel. There she caught the eye of director Joss Whedon, who later cast her in his short-lived TV series Firefly as River Tam, a role she reprised for the show's feature film sequel, Serenity. Glau previously auditioned for the role as a Pink Ranger on one of the Power Rangers series before meeting Joss Whedon.

Glau appeared on the episode "Love Conquers Al" (1x06) of the TV series Cold Case. She had a small role in the film Sleepover, in which she played a high school senior named Shelly. She also appeared in the CSI episode "What's Eating Gilbert Grissom?," and the second season of The Unit; portraying Crystal Burns, the girlfriend of Jeremy Erhart. In 2006, Glau played Tess Doerner, a paranoid schizophrenic returnee in the second season premiere of The 4400 (episode "Wake-Up Call"), and became an essential recurring character from Season 3 onwards. Her character had the power to compel people to do whatever she wanted. She also starred in the science fiction film Mammoth. Glau was cast in a TV movie on AbcFamily called The Initiation of Sarah.

In Terminator: The Sarah ConnorChronicles, a series that debuted January 13, 2008, Glau plays the role of Cameron Phillips, a Terminator infiltration unit sent back to protect John Connor and Sarah Connorfrom Skynet. The seventh episode of the series, "The Demon Hand," included several scenes in which Glau (in character as Cameron) dances ballet. Glau also guest starred as herself in episode 17 of the second season of The Big Bang Theory.