Lancelot

Sir Lancelot was a knight in the service of King Arthur. He was the subject of several works of fiction. The Second Doctor summoned Sir Lancelot in his mental battle with the Master of the Land. (TV: The Mind Robber)

The Fourth Doctor claimed to have taught Lancelot how to use a sword. (PROSE: Wolfsbane)

The Thirteenth Doctor remembered telling a knock-knock joke to King Harold, which she repeated to Harold Wyntonia: "What do you call a knight who always cheats on his tests? Sir Glancelot." (COMIC: Mistress of Chaos)