He was portrayed by the late Rick Aviles. who also played Ratty "Rat Man" Erwins in Stephen King's The Stand.
Willy first appears when he attempts to rob a wallet belonging to Sam Wheat. This results in a fight, and Sam gets killed as a result, prompting Willy to run away as Molly and two newcomers tend on a dying Sam, who dies shortly afterwards on a hospital. Later on, we see that Willy has Sam's wallet, although he fails in getting the codes.
He then tries to break into Molly's apartment to find the codes, but Sam (now a ghost) has a cat to scare Willy into fleeing away from the apartment just as he looked on an oblivious Molly. Sam later finds out that his friend Carl Bruner was the one who sent out Willy to steal Sam's codes to launder money from bank accounts, thus making Carl partially responsible for his death, although Carl didn't want Willy to kill his friend.
Upon hearing that a medium named Oda Mae has withdrawn $4 million from the bank (under Sam's directions), Carl and Willy head over to her apartment to attack her. Fortunately, Sam physically attacks Willy, who then attempts to escape but is killed in a traffic accident.
Willy's ghost arises from his dead body and Sam taunts him by saying, "You're dead, Willy!". A group of howling shadowy demons then appear out of the nowhere and pulled a screaming Willy into the darkness, to Hell for his sins. Carl would later join Willy in Hell some hours later after being stabbed to death in the abdomen by sprinting glass from a falling window while trying facing Sam.
- Despite the fact that Carl Bruner is the main antagonist of the film, Willy Lopez served as The Heavy because his murder of Sam drove the plot of the film, which made Carl the Big Bad and the one behind the plot.
- Nevertheless, Willy is more evil than Carl, as he did not express any kind of remorse for killing Sam.
- Willy must have been a clever mugger, given that he had no criminal records on the New York City Police Department.