When Billy Batson as a young boy, his parents were killed by his future arch nemesis Black Adam (then their assistant Theo Adam) He was separated from his sister Mary Batson who would later become Mary Marvel, and sent to live with his uncle. Unfortunately, his uncle kicked out Billy and stole his inheritance. Living on the streets, Billy sold newspapers until one day, a strange cloaked man lead him to a part of the subway he'd never seen before. A marvelous train awaited them, covered in hieroglyphs and runes. Billy and the stranger rode the train deep into the bowels of the Earth and into a cavern that contained statues of the Seven Deadly Enemies of Man pride, envy, greed, hatred, laziness, selfishness, and injustice. There, he met the ancient wizard who had protected mankind from them for thousands of years. His name was Shazam and he had chosen Billy to succeed him and granted him all of his extraordinary powers by speaking his name. Shazam stands for Solomon=Wisdom, Hercules=Strength, Atlas=Stamina, Zeus=Power, Achilles=Courage, Mercury=Speed.
Due to trademark issues with using the name Captain Marvel (with Marvel Comics, no less), DC has been forced to use Shazam as his name in marketing (this is most prominent on the website of Mortal Kombat vs. DC Universe, where there is even a take of the game's announcer calling him Shazam). Following the new 52 comic reboot, it seems that his superhero name is now Shazam altogether.
Mortal Kombat vs. DC Universe
Captain Marvel is guided by Shazam through a focusing ritual to regain control of his powers. At its apex, Captain Marvel found himself meeting the Elder Gods. He then begins to learn these gods' newfound powers.