War Master

The Master was ressurected by the Time Lords during the Last Great Time War, because they believed that he was a good soldier. He was assigned to protect the cruciform but was scared and ran away to the end of the universe becoming Professor Yana. Years later, Martha Jones helped the Professor to notice his fobwatch, despite the perception filter, and he opened it, becoming the Master again. He allowed the Futurekind to enter the silo. He attacked Yana's assistant, Chantho, who shot him before he she died. He entered the Doctor's TARDIS and regenerated into his next incarnation.