Pandad IV

Goth, having become Chancellor, expected to succeed but the Time Lord President, but he informed him he would choose someone else, leading Goth and the Master to assassinate him before he could make his announcement.

Behind the Scenes

 * Given the average reign of a Time Lord President lasts a few centuries, it seems likely that this was the same President who had been challanged by Omega a few years earlier, possibly having regenerated.