The Kryptonite Man started as the Kryptonite Kid, an alien juvenile delinquent who accidentally became charged with kryptonite radiation in deep space. With a super-power that allows him to kill Kryptonians, the Kid decides to harass the last Kryptonian - Superboy. Superboy easily outsmarts the Kid, which proves juvenile delinquency doesn't pay.

The Kryptonite Man only makes one appearance that I know of - in Alan Moore's "Whatever Happened To The Man of Tomorrow?" story. It's well worth reading, and not just because of the Kryptonite Man.

The Recipe

The Kryptonite Man is a repainted Minimate. His skullcap and ears are made from Sculpey. His face and costume details are digital printouts.