Billy Chambers is a convicted felon who ran away from the USA 8 years ago and has hid out in Mexico. His only real friend seems to be his pet chihuahua named Moco. 4 years prior to the events in Once Upon a Time in Mexico , He began working for Barillo and eventually became his right-hand man. Billy is found by (Retired) FBI Agent Jorge Ramirez and is willing to go quietly. Billy does not like what Barillo is doing nor what Barillo instructs him to do. Billy eventually confronts Barillo and is shot in the back and killed.