Descended from Gallifreyan colonists on the planet Diomedes, the Diomedeans are more divergent than the Gallifreyans or the Llinyari.

What distinguishes a Diomedean from a blue Gallifreyan is the yellow eyes and sharp teeth. Diomedeans are mostly nocturnal, and are exclusively meat-eaters.

In general, they are more solitary than Gallifreyans, and it is not uncommon to find only one or two per ship.