|The following is based on Fallout: Brotherhood of Steel and is not canon.|
The Wasteland Stranger is a mad man wielding a very powerful turbo electric plasma rifle, to kill his opponents. If all other combatants in the arena have been defeated by the Initiate, the Wasteland Stranger can be fought as the final challenge, and the reward for defeating him is 50000 caps. The stranger says no words, and is probably not only kept alive by the Church of the Lost to fight in the arena, but also enjoys it.
The wasteland stranger appears only in Fallout: Brotherhood of Steel.