Dax Fex Fize Gossimar Day Slitheen was a male member of the Slitheen family, married to Bloorm Vungah Bart.
Dax posed as Jay Stafford and attempted to avenge his family after their defeat by Sarah Jane Smith. Whilst breaking into his house, Maria and Alan Jackson discovered a body hung up, like a piece of clothing. After revealing this to Sarah Jane, they set off to stop Dax, Bloorm and Korst Gogg Thek. After discovering the true motives of the Xylok, Mr Smith, Dax and Bloorm decided to help and they formed an alliance with Sarah Jane, Alan and Maria. Ultimately, Mr Smith's plan was foiled, and the three Slitheen left Earth. (TV: The Lost Boy)
Daz Fex Fize and his wife's branch names are never given, although Dax Fex Fize's middle names are identical to that of Glune Fex Fize Sharvaleer-slam slitheen meaning that it is possible that Dax Fex Fize hails from the Sharvaleer-slam branch.