First Great Time War

The Black Sun War was a time war fought between the Gallifreyans (and later the early Time Lords) against the Order of the Black Sun, based thirty thousand years in Gallifrey's future.

History
The first strike of the war, from the Time Lords' point of view, was when a Black Sun agent travelled back in time to attack and prevent Omega and Rassilon from turning the star Qqaba into a power source for their time experiments. The attempt did not succeed but did cause the apparent death of the stellar engineer; Omega. (DWM: Star Death)

The Time Lords did not know why the Black Sun (whom they had never encountered before the attack) should have wanted to strike at them, and surmised that it was for something they (the Time Lords) had yet to do. (DWM: Star Death, 4-D War) Years later, at a diplomatic conference, a representative of the Order was murdered by the Sontarans. The murder was blamed on the Time Lords. This provided the motivation for the war's beginnings, as from the Order's point of view, the Time Lords were the ones who had struck first. (DWM: Black Sun Rising)

Behind the scenes

 * The comic stories comprising the Black Sun arc were an early collaboration between writer Alan Moore and illustrator David Lloyd, who would go on to create the graphic novel V for Vendetta.