Alex Rinaldo is the secondary antagonist of the novel Slimer.
Alex Rinaldo was a Mexican-American acquaintance of Paul Latham and Mark they met while in the US. He'd been in the military once, but had been dishonorably discharged for drug use. A cutthroat thug who carried a switchblade, Alex persuaded the two Englishmen to do a dope run across the Atlantic. Alex went with them, and brought his girlfriend Rochelle along. When Mark's yacht, Alex and Rochelle joined in the others in escaping aboard a life raft. While they were adrift at sea, Alex tried Paul's patience by repeatedly challenging his authority, making overt passes at Linda Warner, antagonizing both him and Mark, and generally just being a nuisance. This behavior continued unabated once the castaways were aboard the Brinkstone rig, and even got steadily worse.
Because Mark was a heroin addict, his girlfriend Chris pleaded with Alex to let her sick boyfriend have some of his drugs, as, by this point, Mark was experiencing withdrawal. Alex agreed, but only after Chris performed numerous sexual favors for him. He also got drunk and attempted to rape Linda in the rig's rec room, but she and Chris were able to lock him out. Encountering scientist Dr. Carol Soames, Alex attempted to have his way her, too, but recoiled when she turned out to be the genetically engineered shapeshifting shark Charlie in disguise, and stabbed "her" and ran. When he returned with the others, "Soames" was gone.
Sometime later, after the group's first real encounter with Charlie in the form of Brinkstone security guard Ed Buckley, the injured Rochelle was taken while she was in the cabin she shared with Alex, and became part of Charlie. The shark took on Rochelle's form and seduced Alex when he came into the room, ultimately killing and absorbing him. Alex's strong-willed personality allowed him to overtake that of Charlie, and he forcibly transformed the shark's malleable body into that of his own, and, while in control of the body, raped, killed and ate Chris. However when he attempted to do the same thing to Linda, Charlie reasserted control, and Alex's mind became trapped. Later, he was freed when Paul and Linda killed Charlie's original body, granting Alex and Charlie's other victims the release of death.
In the movie based off of the novel, Proteus, Alex is a heroic character and the protagonist. He is also no longer Mexican-American but British and played by Craig Fairbrass, and survives.