First of the Time Lords

By some accounts, Rassilon was known by the epithet "First of the Time Lords". (PROSE: The Legacy of Gallifrey, COMIC: The Forgotten) One account presented a young Rassilon as commanding the Gallifreyans when they were known as Space Lords. (COMIC: Monstrous Beauty)

During the First Omega Crisis, Omega insisted that he alone was responsible for his people mastering time travel and thus becoming Time Lords. (TV: The Three Doctors) Indeed, in one version of reality glimpsed by Omega, the Time Lords became "gods" thanks to him as there was no Rassilon at all. (PROSE: The Infinity Doctors)

By one account, this was because Rassilon experienced the first regeneration on Gallifrey. (PROSE: The Legacy of Gallifrey) By another account, the Timeless Child was the first to regenerate. (TV: The Timeless Children)

When the Tenth Doctor, who considered himself the last of the Time Lords, saw the Seal of Rassilon, he recalled that Rassilon was the "First of the Time Lords". (COMIC: The Forgotten)

Swarm identified the Thirteenth Doctor, who had earlier been the Timeless Child, as the "first Time Lord", and offered her as a sacrifice to Time. (TV: The Vanquishers)

The Father of Time identified himself as the one who had kept watch over Time itself before the inception of the earliest Time Lord. The First Doctor, after passing the Test of Time, recognised the Father of Time as a future incarnation of himself. (COMIC: The Test of Time)