A man who stole a spider's gifts in the Amazon in 1973, saw his own death, and set out to kill the three girls he saw in it first.
Ezekiel Sims is the man Constance Webb hired for protection when her research team went into the Peruvian Amazon in 1973 looking for a spider with rare healing properties. Tahar Rahim plays him in Madame Web. He betrays the team, shoots Constance in a struggle and claims the spider for himself; from it he gains enhanced strength and health, and a limited clairvoyance that shows him his own death. It leads him to hunt three young women who have the potential to become Spider-Women, obsessively, before they can become it.
He can inject a neurotoxin into anyone he touches, and wears a black and red suit that Wikipedia describes as similar to Spider-Man’s. He is, in short, the film’s Spider-Man, on the wrong side.
Minor spoiler
Cassie Webb, Constance’s daughter, keeps getting between him and the girls: at Grand Central, at a diner, at a hospital. In the end the group lures him to a condemned fireworks factory and sets traps to disorient him, and Cassie guides the girls out and lures him into the last one.