Rufio is a male Breton who resides in the Inn of Ill Omen. You must kill him in the quest to join the Dark Brotherhood, A Knife in the Dark. In the quest The Purification Lucien Lachance gives you a scroll that can summon the ghost of Rufio.
Rufio also raped someone (can't remember her name right now) which explains why the Dark Brotherhood wants you to kill him.
Related ThreadsRufio - last post by @ Apr 2, 2006
Heh..I lost Rufio - last post by @ Aug 6, 2007