Giant-Man

Giant-Man (aka Hank Pym; formerly Ant-Man) is one of the founding members of the Avengers.

Formation of the Avengers
As a result of Loki's meddling, Ant-Man and the Wasp  accidentally intercepted a distress call from the Teen Brigade regarding a situation involving the Hulk. Iron Man and Thor had also responded to the signal and worked to subdue the Hulk. When Loki was revealed as the true cause of their troubles, the four heroes worked together to bring him down. Seeing how much more effective they worked as a team than solo, the group decided to stick together and call themselves the Avengers.

Giant-Man
Hank Pym not only has the power to shrink to the size of an ant, he can also grow to be giant in size. Upon using his powers in this new way, Hank Pym adopted the name of "Giant-Man."

Powers
Through his helmet, Ant-Man can communicate with and command ants and other insects to do his bidding.

Ant-Man can change sizes by ingesting special caspules that he invented. By taking "growth pills," Ant-Man can return to his normal size.