The War Lord was the leader of the War Lords who made an alliance with the War Chief to kidnap humans to participate in the War Lords' war games.
He was eventually tried by the Time Lords and was sentenced to be dematerialised out of existence, along with all War Lords. (TV: The War Games)
In an alternate timeline, the War Lord was able to conquer the entire galaxy with his human army, due to the Doctor being removed from existence. (AUDIO: The Light at the End)