A Wanderer

 is a hostile NPC in Fallout 3.

Accompanied by three Raider Guard Dogs, the raider is usually found east of Roosevelt Academy in the vicinity of what appears to be his/her camp.

He/she is in possession of the Wanderer's Leather Armor, a unique Leather Armor, and armed with a Sawed-Off Shotgun.

Locating the Wanderer
The Wanderer is found between Roosevelt Academy and Paradise Falls. Due east of the Academy's Arts and Athletics Hall is a car pile-up, and directly north of the bus in that pile-up is a two-level platform or 'jetty', presumably the Wanderer's home. See the gallery below.

Inside and around it is some food, ammunition (a Mini-Nuke under the table on top of the house) and two relatively rare Dog Bowls. The body of the wanderer may sometimes be found directly opposite this platform on the opposite river bank.

Trivia

 * The Wanderer might be a nod to the Mad Max movies.