Parasite

Joshua Michael Allen was originally a bike courier from Metropolis, until an alien flu granted him the power to absorb other people's power. His life changed when he crashed into a green blob and suffered electric shocks, and then he lost consciousness. He awoke in the hospital, where he was diagnosed as suffering from alien flu.

Then he was called into S.T.A.R Labs, where he was checked for a virus. But an explosion killed all the doctors and transformed him into Parasite. As Parasite, he drained the life of people around him, and he wanted to kill himself. However, the Man of Steel came just in time and when he touched Superman, he gained incredible strength. Therefore, leeching metahuman powers became his new obsession.