A student who can control fire but cannot make it, which means he always needs a lighter and always needs somebody to give him one.
John Allerdyce can manipulate fire but not create it, so he carries a Zippo everywhere, and that single limitation is the most efficient piece of character writing in the first three films. He needs a source. He is always looking for one, and Magneto is happy to be it.
His defection at the end of X2 is the series at its most economical: the school is a place that keeps telling him to hold back, and somebody finally tells him not to.
Minor spoiler
In Deadpool & Wolverine he shoots Cassandra Nova, tells her about Paradox’s plan, and is killed by her for it.