Captain Universe is a title similar to Green Lantern. Sorry to mix my universes, but it's the quickest analogy I could think of. No one person is Green Lantern. The Green Lantern is whoever the ring chooses. That's the same with the the energy that makes Captain Universe, well, Captain Universe. Some alien/celestial beings from another world sent out the energy (the Uni-Power), but no one really knows anything about them, so screw 'em.
At one point the Uni-Power found Spider-Man, though he didn't get all of the powers. It's a good thing he got them though, because his next set of battles would require all of the power he could get. Some people get all the luck. Not only does Peter Parker get bit by a radioactive spider, he gets the Uni-Power too. I can't even get a good parking space.