Fenris

 (also known as the Hellbringer) was an agent of the Order of the Black Sun. He travelled back in time to sabotage the initial Gallifrey time travel experiments at Qqaba. Fenris caused the statis halos on Omega's ship to fail, making Omega fall into the black hole. Rassilon's intervention, however, dispatched Fenris and the experiment worked. Fenris’ discarded belt provided the much needed technology to use the new energy and could also be used as a form of directional control. (COMIC: Star Death)

Twenty years after the loss of Rassilon, the Time Lords tried to free Fenris from the Zone of No Return so as to find out who sent him. But before they could learn anything, they were attacked by members of the Order of the Black Sun, who killed Fenris and some other Time Lords before vanishing. (COMIC: 4-D War)