I have a few concepts I've been batting around. This one is my current favorite. If it doesn't fly let me know and I'll work on one of the others.
Nanite
John Tyler is a normal college student who attempts to make a quick buck by signing up for an experimental drug trial. However, instead of receiving his drug, John becomes an unwitting dupe for industrial espionage.
There is an underhanded doctor working on a secret nano technology project at the same company developing the test drug. He cannot remove the nanobots from the labs himself, the workers are watched too closely. Instead he contrives to inject them into John, intending to kidnap him and forcibly remove the technology once it was safely outside. Much to his chagrin, he is discovered before he can make good his plans, but not before the nanites are injected into our ususpecting hero.
Sadly, the plan would not have worked in any case. Once adapted to a host, the nanites become inert if removed. Forced with losing a fortune and countless years of research, the firm strikes a deal with John where he becomes the newest test subject for their nanotechnology. He takes it out into the streets on Freedom City and puts it to real use.
The nanites inside him are incredibly sophisticated devices, improving on John's natural abilities, keeping him healthy and repairing any damage. But their most versatile function is their ability to reconfigure into a limitless number of devices for any conceivable purpose.
Basically, in addition to improved physical abilities and regeneration, the nanites would also produce a limited shapeshift type effect where he creates specific effects one at a time with nanite devices. Jetpack, laser, armor, those kind of things.