Dak Fex Fize Gossimar-Day Slitheen was a male member of the Slitheen family, married to Bioo Goo Von Bar.
Biogrpahy
Dak posed as Jay Stafford and attempted to avenge his family after their defeat by Sarah Jane Smith. Whilst breaking into their house, the Jackson's discovered Jay Stafford's body hung up, like a piece of clothing. After revealing this to Sarah Jane, they set off to stop the three Slitheen. After discovering the true motives of the evil Xylok, Mr Smith, Dat and Bioo decided to help and they formed an alliance with Sarah Jane, Alan Jackson and Maria Jackson. Ultimately, Mr Smith's plan was foiled, and the three Slitheen left the planet.