His name's Richard Rider. He got his powers from a dying member of the Xandarian Nova Corps, an intergalactic police force, and initially used them as a superhero on Earth. He was recalled to active duty in the Nova Corps and ventured out to Xandar, where he eventually had to relinquish his powers. He came back to Earth and lived a normal life, but unbeknownst to him his powers were only dormant. Night Thrasher dropped him off a building hoping that a high-stress situation would force his powers back out, and it worked. Nova helped Night Thrasher found the New Warriors and stayed with the team through most of its various incarnations while simultaneously soloing and occasionally helping the Nova Corps.
He left the team to return to Xandar at the Nova Corps' behest just before the Annihilation Wave hit, destroying Xandar and almost the entire Nova Corps. The Xandarian Worldmind, a computer containing the collective knowledge of the Xandarians, merged with Richard and imbued him with the Nova Force, the source of all the Nova Corps officers' powers. Housing all that power and knowledge pushes Richard's mind to the limit, but he meets up with Drax, who shows him how to control them. Nova then fought to save a few survivors from the Annihilation Wave with the help of Drax and Quasar. Quasar sacrificed his life fighting Annihilus himself to save Nova, Drax, and the survivors. Nova later winds up leading the United Front, a ragtag army comprising remnants of the Skrull army, Kree opposed to House Fiyero, some ex-heralds of Galactus, and various survivors of other races who were hit by the Wave. They're quickly losing the war but Nova manages to find and kill Annihilus, which ends the war and allows an uneasy peace to be forged.
Nova's new comic picks up with Nova returning to Earth after the Annihilation War. Go now, purchase the comic, read it, and be merry.