Tricia Janine Helfer is a Canadian and American actress. She is known for portraying Number Six in the science fiction series Battlestar Galactica (2004–2009). She also voiced Sarah Kerrigan in the video game StarCraft II and its expansion packs (2010–2015), and portrayed Charlotte Richards/Goddess in the urban fantasy series Lucifer (2016–2021).

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.