Superman was killed in the comics by a creature named Doomsday. The Creature is from Krypton: Superman's home world. In the show Smallville, it shows that General Zod sent Doomsday to Earth, the same time Kal-El aka Superman came. He attached it to his ship. In the comics Superman does get killed by the Doomsday creature, but Superman manages to stop Doomsday from destroying the city.