Number Six is a family of fictional characters from the reimagined science fiction television series, Battlestar Galactica. She 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.
Battlestar Galactica chronicles the journey of the last surviving humans from the Twelve Colonies of Kobol after their nuclear annihilation by the Cylons. The survivors are led by President Roslin and Commander Adama in a ragtag fleet of ships with the Battlestar Galactica, an old but powerful warship, as its command ship. Pursued by Cylons intent on wiping out the remnants of the human race, the survivors travel across the galaxy looking for the fabled and long-lost "thirteenth" colony.