Ytraxorians were native to the planet Ytraxor. They were natural ocean-dwellers, but were able to walk on land. Their culture was a caste system, the people genetically engineered to be one of two groups: the warriors and the elite.
When their planet slowly froze as its sun grew cold, the Ytraxorians huddled in caves to avoid the encroaching glaciers. Ytraxorian scientists developed the Ytraxorian Reality Gun, which sent its target through time and space. The Ytraxorian ArchDuke approved the rifles for use. The Ytraxorians used the rifles on each other, swiftly wiping out their species until none remained.
One Ytraxorian was transported to Torchwood Three's Hub, where it soon died after transporting into a deep-fat fryer. The Ytraxorian told Jack Harkness of its people's history before its death. (PROSE: The Men Who Sold the World)