Tremas of Traken was one of the five consuls to the the Keeper of the Traken Union and at one time a candidate for Keeper. His body has later taken over by the Master. He also fathered the Doctor's companion Nyssa.
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Tremas married Kassia, his second wife, who was also a consul. Together they 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. The Master, who still possessed some of the Keeper's powers after being removed from the Source, took over Tremas' body to use as his fourteenth incarnation. (DW: The Keeper of Traken)
- For further details on this merged identity see separate article.