First Rank
From Tardis Wiki, the free Doctor Who reference
Morbius, who had once been Lord President, claimed to be a "Time Lord of the First Rank" (TV: The Brain of Morbius) as did the Master. (PROSE: First Frontier)
Retro-regeneration, the re-visiting of previous incarnations, was said to have only been attempted by Time Lords of the First Rank. (PROSE: State of Change)
