The Death is a rogue Time Lord, father of The Beginner.
Test of a Time LordEditThe Beginner went through the test of a Time Lord, and spoke of how his family died in it, including his father. His body was also seen, but was later proven to be fake. (Test of a Time Lord Part 1, Like Father Like Son).
The End of the WorldEdit
The Death wanted to end the world in the year 2012 in order to make space for Gallifrey to return (Like Father Like Son). He somehow managed to present himself as a voice in people's minds, like the Aztec man and Jo. He had many obstacles for The Beginner and Jo along the way, like the mummy, and the cave of curses. (2012, Like Father Like Son, Cave of Curses). Finally, in a duel, he was killed by The Beginner, as it was the only way to stop his plans. He was not seen regenerate, and his body later thrown into a nearby river. (Time Lord Duel).
After the events of his 'death', he waited until he was out of view and decided to regenerate. He then somehow made his way to Cybermen in which he formed an alliance in order to take over Earth and get revenge on the Beginner. The Beginner with help from Spike Dimentos and The Writer formed an army to finally take him down. (Battle of the Beginner)