Fourth Master

The Fourth Master is the fourth incarnation of the Time Lord known as the Master. He emerged after the Third Doctor died, due to his old age. He was obsessed with the Doctor, especially with the Seventeenth, whom he never met.

As time passed, he came to hate his new body, and decided to hide and create a disguise. He called himself "the Trickster" and used his ability to time travel to mess with people's timelines.