Pyro is a mutant in the Marvel Universe. His real name is St. John Allerdyce. Born in Sydney, Australia, his mutant powers emerged in his teens, but he could not think of a practical way to use them. Pyro's power is the ability to manipulate any flame within a certain radius by forming it into any shape he desires, or increasing or decreasing its heat, intensity or size. His only limitation is that he cannot actually create fire - in the comic books he often carries a flamethrower into battle, and in the movies a young Pyro is shown always carrying a lighter. Pyro cannot be burned by any fire he controls, but if he turns his attention from it, it will revert back to normal flames and can harm him. Pyro's fiery "creatures" have a greater solidity than normal flame, so a giant flame "bird" that Pyro creates would be able to pick up something and carry it in its talons.

After years of working in Southeast Asia as a journalist and novelist, Pyro met the mutant Mystique, who later recruited him to be a part of the Brotherhood of Evil Mutants. He served in this team under several leaders, including the Toad, but not under Magneto, its original leader. Mystique's Brotherhood later offered its services to the United States government, in exchange for protection and a pardon, and became known as Freedom Force.

Some years ago, Pyro contracted the Legacy virus, a fatal disease only mutants can get. He committed several crimes in attempts to find a cure, but was not successful. He died just after saving Senator Robert Kelly 's life from a new Brotherhood of (Evil) Mutants, but the Senator was shot and killed soon after by a human-supremacist.

He was played by Aaron Stanford in X2 (The second X-Men movie). In the movieverse, as opposed to the comics, Pyro is American rather than Australian and attends Professor Xavier's School for the Gifted before joining Magneto's Brotherhood.