Threkker was a member of the Epsiloni, a race of beings who absorbed the life-forces of organic species. He was imprisoned in a black hole, but managed to escape and landed on Earth on the farm of Jim Hendricks. When warships were sent after him, Captain America helped him fend off the robots that were trying to retrieve Threkker until Cap realized that he was planning to absorb the life forces of everyone on Earth. He was imprisoned once more and thrown into the star Epsilon Four shortly before it went nova.
He was captured by the enigmatic alien, the Stranger, and was imprisoned in the Stranger's Labworld for the alien to study him. He remained there until freed by Overmind.