Emperors of the Third Imperium/meta
During the period of the OTU covered by the MegaTraveller rules, Strephon is assassinated in 1116, and many groups claim to be the rightful successor and help perpetuate a civil war. See Successors to Strephon. The TNE rules covers the period of time after the fall of the Third Imperium.
In the GURPS Traveller universe, the assassination of Strephon never happened, and the civil war never broke out. Thus, in GT, there is no successor to Strephon.