Rassilon is a fictional character in the British science fiction television series Doctor Who. In the backstory of the programme, he was the founder of Time Lord society on the planet Gallifrey and its first leader, as Lord High President. After the original television series ended in 1989, Rassilon's character and history were developed in books and other media.

The Time Lords are a fictional ancient race of extraterrestrial people in the British science fiction television series Doctor Who, of which the series' main protagonist, the Doctor, is a member. Time Lords are so named for their command of time travel technology and their non-linear perception of time. Originally, they were described as a powerful and wise race from the planet Gallifrey, from which the Doctor was a renegade; details beyond this were very limited for the first decade of the series. They later became integral to many episodes and stories as their role in the universe developed. For the first eight years after the series resumed in 2005, the Time Lords were said to have been destroyed during the Last Great Time War at some point in the show's continuity between the television movie in 1996 and the show's revival. In 2013, the 50th anniversary special "The Day of the Doctor" concerned this supposed destruction and their eventual survival.