Wadsworth

 is your personal Mr. Handy butler in Megaton, which you get, together with a house, for disarming the nuclear bomb that lies in the middle of the town. He can give you instructions on how to spruce up your house, give you haircuts and tell science-related jokes (only a few at a time, so he can recharge his 'humor emitter array'). Wadsworth can also give you Purified Water, but only up to five at a time before needing to recreate his supply. It takes a week for him to recreate his supply.

If he follows you up to your bedroom, he can get stuck in there for a long time. He can stay in the room for up to around two weeks before he moves.

When you buy the My First Laboratory and ask Wadsworth to explain what it does, he'll explain that it can be used to remove addictions, and then add under his breath (without appearing in the dialogue subtitles) "knowing what you're addicted to it might blow out the program all together."

Also, when you approach him, one of his phrases is "How may I serve you Master?" Followed by (again not in the dialogue subtitles) "not that I really want to.."

His name is a reference to Tim Curry's Character "Wadsworth The Butler" in the movie "Clue".

Appearances
 appears only in Fallout 3.