When Superman fights the cyborg Metallo, Luthor intervenes. In Superman (vol. 2) #2, discovering Metallo is powered by a 'heart' of kryptonite that can hurt and potentially kill Superman, Luthor steals it and a creates a kryptonite ring for himself. He wears the radioactive ore around his finger as a symbol that he is untouchable, causing the Man of Tomorrow pain and weakness whenever he approaches. Not realizing humans can be affected by severe or long-term meteoric radiation exposure, Luthor eventually suffers from Kryptonite poisoning. He had his right hand amputated to prevent the cancer's spread, and not long afterwards, said kryptonite ring (which he kept in cold storage prior to the surgery) would be stolen. Eventually coming into the possession of Superman, who in turn entrusts it to Batman, tasking the Dark Knight to use it if the Man of Steel ever becomes corrupt or falls under the control of another. But removing the tainted limb was a mere half measure, as his affliction had already metastasized rendering Lex's condition terminal.