Kryptonite Man

Kryptonite Man is a human being who was altered by an accident into living Kryptonite. He holds a particular grudge against Supergirl, who was the first Kryptonian he fought and was defeated by after getting his power, though he also ironically has a grudge against Lex Luthor.

Dr. K. Russell Abernathy was a scientist who developed a Kryptonite isotope enhancer, in order to take Kryptonite radiation and convert it into useable energy (for something other than killing Superman). When the isotope enhancer overloaded, it caused a massive explosion of Kryptonite radiation throughout his laboratory. Instead of dying, the radiation mutated him into a being that emanates pure Kryptonite, as well as unhinging his mind quite a bit.