Dr. Leeds got a sample of meteorite from the planet Krypton which fell to the Earth. When Clark Kent arrived to see the glowing sample, he apparently fell dead immediately. When the Kryptonite was recovered, Clark recovered, and revealed his identity as Superman, asking Leeds to discard the Kryptonite. Leeds agreed to throw it in the ocean after a few days of study. ("Superman")
- Leeds may be based on the character of Barnett Winton, the astronomer who identifies Kryptonite in The K-Metal from Krypton, an unpublished comic story which features the first appearance in any form of Kryptonite, unless one counts the strange meteor used by Professor Smalley in Reign of the Superman.