Rassilon was one of the founding members of Time Lord society, and has served as President, Lord President, and "God Emperor" of Gallifrey on multiple occasions.
- Rassilon's history prior to their appearance in The Game of Rassilon can be found on the TARDIS Data Core.
At some point, Rassilon returned to Gallifrey where he once again became President.
Rassilon appeared at Colony 47 to intervene when the colony began to collapse the boundaries between realities. Once there, he arrested the Doctor, Travis and Millie. He revealed that Colony 47 was, in fact, Skaro - Rassilon had erased the Daleks from history, "because [he] cannot be stopped." (Getaway)
He took the trio back to Gallifrey, where he tortured the Doctor, imprisoned Travis, and returned Millie to her own time, bringing her death forward from 1937 to 1932. (Active Decay)
During this time he also found the other Travis inside the Matrix, the other Travis having piggybacked into their reality in Travis' mind, then jumping into the Matrix from there. (Both Ends Burning) Rassilon appointed the other Travis as Keeper of the Matrix, and presumably set him to work building the Perfector. (Perfection)
With the Perfector complete and his victory assured, Rassilon sat in his throne room eating oranges, believing that when the Perfector was fully activated whoever sat on the throne would become "it." By this time, he was referring to his position as "God Emperor of the Time Lords".