Tremas

Tremas of Traken was a one of the five consuls to the Keeper of Traken and was once selected to become Keeper. He married Kassia, his second wife, who was also a consul, and he had a daughter, Nyssa.

However, Kassia came under the influence of the Melkur and she turned against the Traken Union. When Tremas was considered unfit to become Keeper for helping the Doctor and Adric, Kassia was chosen and when she became connected to the Source, the power of the Keepers, she was destroyed and replaced by the Melkur, who it was revealed was really the Master

Tremas helped the Doctor to stop the Master and still save the Source. In an unfortunate outcome, the Master, who still possessed some of the Keepership's powers after being removed from the Source, took over Tremas' body to use as his thirteenth incarnation. He would use Tremas' body as his own until he faced the Doctor on the Cheetah World. (DW: The Keeper of Traken/Survival)