History
Brian was a young mutant who lost control of his powers and leveled a significant part of Port Washington, New York in the process. The X-Men came to rescue him but before they could he was shot by one of the townsfolk. Nightcrawler whisked him to hospital to save his life.
He later recovered and deeply regretted his actions, wishing to find a way to prevent his mutant powers. Kitty Pryde instead suggested that he shouldn’t live in fear and could join the X-Men.
Powers
It’s been claimed that Brian is an Omega-level mutant. Certainly his fiery energy discharges are enough to cause widespread destruction.