You may be looking for No. 1, a mission in Grand Theft Auto IV.
No. 1 (not to be confused with Zero) is a resident of Liberty City in 1998, and is most known for his appearences as hitmen. In the mission, No Son of Mine, Ma Cipriani issued a hit on her son, Toni Cipriani, No.1 poses as the hitmen who are searching for Toni. They also appear in Grand Theft Auto Vice City Stories, posing as hitmen against multiple people. In both editions, No. 1 is a playable multiplayer character.