Henry “Hank” Pym was a scientist who created two serums: one that could shrink things to a fraction of their size and the other which could return them to their original size once more. He invented them as a solution to the high cost of shipping as well as making the transportation of military men and equipment less complicated a task.
Pym realizes that in order for the serums to be used on soldiers, he would first have to test them on himself. Unfortunately, the formula worked too fast and shrunk Pym to a much smaller size than he anticipated. He shrunk to the size of an ant.
Some ants spotted him and began chasing him. Cutting off all other avenues of escape, Pym ran up the ant hill and dropped down into it. When he landed in and became stuck in some honey, a miraculous thing happened – an ant extended a leg for him to catch on to and pulled him free of the sticky mess.
No sooner was he free, however, than he found himself surrounded by the other ants again. He spies a white-tipped wooden match sticking up out of the ground, and in desperation, threw a rock at it. The rock skipped across the tip of the match, igniting it.
While the ants were confused by the fire, Pym escapes back outside. He looked up and saw the test tube of serum that would return him to his normal size perched precariously on the window ledge far above him.
Then he noticed the ants were all coming up out of the anthill, closing in on him. But at the last second, one ant, the same one who had pulled him from the honey, helps him. He climbs onto its back and it carries him up the wall to the test tube.
Pym quickly bathed himself in the serum and immediately returned to his normal height. The first thing Pym did was to pour the rest of the serums down the drain, realizing that they were much too dangerous.
But shortly after this experience, Dr. Pym became extremely interested in ants. He created a cybernetic helmet which he could use to communicate with and give orders to ants. He also brought back his shrinking formula in order to be able to more closely observe them when he communicated with them, and a special suit that would protect him in case any ever posed a threat to him.
Eventually, he met Janet Van Dyne and recruited her as his partner, The Wasp.
Later, he created another serum which allowed him to grow from his normal height to several stories tall. From this point on, he called himself Giant-Man.
Later still, he would take on other personas, including Goliath and Yellowjacket.