Order of the Black Sun

The Order of the Black Sun was a group that waged a time war against the Time Lords, the first time war the latter had ever fought.

Membership
Several different species, some humanoid, others only vaguely humanoid, made up the Order. They wore capes and black unitards with a logo on them. (COMIC: 4-D War, Black Sun Rising) They used hand-held black orbs as the focus for blasts of power. (COMIC: 4-D War)

They were represented by an Elder, as well as representatives for different space sectors. (COMIC: Black Sun Rising)

Time War
30 years after the disappearance of the Time Lord Omega, they sent ambassadors to trade with Gallifreyans and Sontarans. Their Elder was killed because of a Sontaran plot, whose fault fell on the Gallifreyan delegation. The diplomatic incident triggered a conflict against the Time Lords. (COMIC: ''Black Sun Rising)

About 30000 years later, they had developed a time travel technology, the time-jumper, with which they sent back an agent to prevent the birth itself of the Time Lord civilisation, but they failed, inadvertently helping Rassilon to develop time travel. (COMIC: Star Death)

20 years after the disappearance of Omega, a group of them showed up on Gallifrey to stop the telepathic parahuman Viridian from unearthing information from Fenris the Destroyer's ruined mind. 11 people on the Gallifreyan side were killed, including Viridian and Fenris. (COMIC: 4-D War)

Aftermath
Long after the time war, a member of the Order of the Black Sun would serve as a High Evolutionary. (COMIC: The Final Chapter)

Behind the scenes

 * Alan Moore mentioned that he intended the Order as a reference/tribute to DC Comics', identifying them as originating from Earth-5's reality (as opposed to DC Comics multiverse, whose main realities were Earth-1 and 2).