Nazir is a  Redguard member of the Dark Brotherhood. After the entrance quest, Nazir is the one who gives the Dragonborn their first set of missions/contracts. Early along in the Dark Brotherhood questline, Nazir can be typically found on the lower level of the Falkreath Sanctuary in the dining room, usually sitting on a chair. Later on, however, his location changes to the Dawnstar Sanctuary. His voice should be smooth, deep, and clear.