Billy Batson was born in New York City in 1930. When he was approximately six months old, his parents were killed in a car crash, and Billy went to live with his uncle, Ebenezer Batson. Uncle Eben wanted nothing to do with the boy, and eventually kicked him out of the house, forcing him to fend for himself on the city streets. By 1940, Billy had managed to secure himself a part-time job as a newsboy.
One evening as Billy was hawking newspapers, a strange shadowy man in a long coat approached him. He beckoned Billy to follow him, and led him underground into a dilapidated subway station. A driverless subway car unlike any Billy had ever seen before, roared to the platform and the two got on board. The car sped off deeper underground, bringing them to a vast cavern known as the Rock of Eternity. Billy disembarked and both the subway train and the cloaked stranger disappeared. Before him Billy saw two rows of statues lining each side of the cavern. Each statue was forged in the likeness of a horrific monster, representing the Seven Deadly Enemies of Man.
At the anterior of the cavern, he found an old man with a flowing white beard sitting on a stone throne. Above him was a large boulder suspended from the ceiling of the cavern by a tiny, fraying thread. The old man introduced himself as a wizard named Shazam, and told Billy that he had been chosen to be his champion against injustice. The wizard lit a brazier to the left of the throne, illuminating the names of six mythological elders inscribed on the wall behind it; Solomon, Hercules, Atlas, Zeus, Achilles and Mercury. He explained that each of these elders would bestow an aspect of their power unto Billy, and all the boy had to do to acquire such power was to speak the wizard's name.
Billy spoke the name "Shazam", and a bolt of mystic lightning struck down from nowhere transforming the ten-year-old boy into a powerful, muscle-bound man. Shazam christened his new champion as Captain Marvel and saluted him.
Moments after the startling transformation, the thread securing the boulder above Shazam's head snapped, and the rock came down, crushing the wizard. Shazam's spirit rose from the debris and told Billy that his ghost would always be present inside the Rock of Eternity, should the neophyte hero ever need his guidance.
Honoring his commitment to the wizard, Billy Batson became the World's Mightiest Mortal – Captain Marvel.