From Grand Theft Wiki

Willy Valerio is the leader of the Northwood Dominican Drug Dealers. He is 29 and originally from South Bohan. He has several criminal convictions, including Grand Theft Auto in 1998, possession of crack cocaine in 2001, and assault in 2005. Valerio is said to be trying to expand the gang's drug dealing horizons but is having serious trouble due to local competition, namely The North Holland Hustlers and Clarence Little's East Holland Drug Crew.

Willy was a close assosiate of Luis Lopez until Luis' arrest years earlier however upon his release from prison, Luis decided to go straight and so he cut all ties with Valerio and the Northwood Dominican Drug Dealers. An interesting note is that Henrique Bardas calls him Willy Valero (evident by the subtitles in-game and by how he says it) forming an unconsistency on how his name is spelt on the police database.