The Warrior's universe

In one parallel universe, the Fourth Doctor chose to destroy the Daleks at their creation. This led to a Time War across the universe, for which the Doctor chose to become the Warrior.

History
During his mission to interfere with the creation of the Daleks, (TV: Genesis of the Daleks) Sarah Jane Smith successfully convinced the Fourth Doctor to destroy the Daleks in the incubation chamber. This alteration to history had massive repercussions, generating millions of aberrant timelines including versions of the Sixth Doctor and Peri Brown similar to those of N-Space. After making his choice, the Fourth Doctor and his companions attempted to retrieve their time ring but were cornered by a prototype Dalek who exterminated Sarah and Harry and mortally wounded the Doctor, who was subsequently extracted by the Time Lords. (AUDIO: Dust Devil) The Doctor's genocidal actions compelled the Kaleds and Thals to come together into the Unified Skaroan Alliance, along with surviving Daleks. Finding the leftover time ring, the Alliance developed time travel and sought to control the universe. (AUDIO: Aftershocks)

Upon being retrieved, the Fourth Doctor was informed by Narvin that the Daleks still existed and the universe was now in the midst of a Time War. Narvin provided the Doctor with an elixir so he could regenerate, with the Doctor deciding to become a warrior. In his new incarnation the Warrior oversaw the termination of the aberrant Sixth Doctor by time bullets. (AUDIO: Dust Devil) Shortly after his regeneration, the Warrior was guided by the Master into sealing off a timeline where the Unified Skaroan Alliance won the Time War and ruled time, containing it in a Carrisent Particum. (AUDIO: Aftershocks)

The Warrior eventually became President of the Time Lords. He initiated a ruthless policy to stop Time Lords travelling back in time to prevent their past selves committing atrocities in the Time War, having the Difference Office intercept and execute them. During his presidency Gallifrey was targeted by the Kraals who were part of the Dalek alliance. Led by Styggron, the Kraals lowered the Time Lords' defences by using an android duplicate of the Sixth Doctor to stir up unrest among the Shabogans to bring down the Capitol's defences, so Styggron could infiltrate the city. Aided by Romana, the Warrior defeated his invasion by using the Relics of Rassilon to atomise the Kraal invasion fleet and, returning a promise he'd made to Borusa, killed Styggron himself. (AUDIO: The Difference Office)