First Doctor

The First Doctor is an iteration of the Unbound Doctor. He stole a TARDIS and ran away.

Biography
A Time Lord (Unbound Universe) from the planet Gallifrey (Unbound Universe), he grew up with the Master and was friends with him while they were in school. One day, he stole a TARDIS and ran away. During his travels, his Unbound Doctor's TARDIS got stuck in the shape of a police box. (Sympathy for the Devil (audio story))

Later on, he landed on Skaro and led the Great Siege, which led to their liberation from their Daleks. (Masters of War (audio story))