Number Six is a family of fictional characters from the reimagined science fiction television series Battlestar Galactica. The character is portrayed by Canadian actress and model Tricia Helfer. Of the twelve known Cylon models, she is the sixth of the "Significant Seven". Like the others of the "Significant Seven", there are several versions of her, including Caprica-Six, Shelly Godfrey, Gina Inviere, Natalie Faust, Lida, and Sonja. She is the only model that does not use one particular human alias for all copies.

Battlestar Galactica (BSG) is an American military science fiction television series, and part of the Battlestar Galactica franchise. The show was developed by Ronald D. Moore and executive produced by Moore and David Eick as a re-imagining of the 1978 Battlestar Galactica television series created by Glen A. Larson. The pilot for the series first aired as a three-hour miniseries in December 2003 on the Sci-Fi Channel, which was then followed by four regular seasons, ending its run on March 20, 2009. The cast includes Edward James Olmos, Mary McDonnell, Katee Sackhoff, Jamie Bamber, James Callis, Tricia Helfer, and Grace Park.