Karl Kreutzfeld was a dedicated Objects collector who showed particular interest in the work of the collectors. He was originally a member of the Legion, but left at an unknown time to search for objects related to the Conroy experiment. By the time Joe Miller had unwittingly gained possession of The Key, Kreutzfeld had nearly all the objects he needed to replicate the Conroy experiment. He believed that he would be able to control the power and use it as a way to bring his son back to life after he died nine years before, although the original collectors had failed to control the power they had unleashed.
After the manager of one of Karl's pawn shops was killed after buying the Key from one of the Weasel's associates, Karl sent some of his men to track down Ignacio Loca, who had taken the key after the attack on the pawn shop in which he worked. Two of Karl's men managed to shoot Iggy as he entered the room via the key, but were unable to retrieve it from him. Iggy appeared in Joe Miller's flat as he died of his wounds, and Joe gained possession of the key.
Karl was obsessed with finding the key before the Weasel, but was sidetracked when Joe and the Weasel broke into his object collection to steal the clock (believing it to be the Prime Object). Karl became enraged as he saw Joe smash down the wall of his object room to reveal a door, and this allowed the pair to escape with the clock via the key.
Knowing that Joe Miller possessed the key, Karl sent his men after him instead. After shooting Joe in the back with a shotgun, (which only stunned him due to the fact that the coat he wore was an object, and therefore indestructible) Karl formed a shaky alliance with Joe after revealing to him the fact that his son had leukemia and the only thing that could cure him was the Glass Eye, a powerful object that had the power to repair and destroy all flesh. He tricked Joe by doing this, neglecting to tell him that his son had died nine years ago and what Joe thought to be his son was in fact an illusion created by the Quarter.
Joe helped Karl gain access to the collector's vault, after retrieving the scissors from Noraida Figueroa. They used the key, the scissors and the clock to break into the vault and claim the objects within. Although Joe did not find the Occupant in the vault, Karl did find what he was looking for - the glass eye. After revealing to Joe his plan to retry the Conroy Experiment, he trapped Joe using a coin illusion of his bodyguard Anthony and escaped with the Key and the Glass Eye.
It is at this point that Karl's sanity is shown to have failed him. He removed his own left eye to replace with the Glass Eye in order to combat the Legion members that were about to attack his home, after being tipped off about the attack by their leader. He vaporised the entire attack force, save for Jennifer Bloom, along with a trio of his own security guards.
As he entered the room, Jennifer Bloom shot him in the chest. He attempted to heal himself, but failed since objects do not work in the room. At this point, Joe Miller arrived in the Weasel's car with the Occupant to stop him, after Joe escaped the collectors vault using the Bus Ticket loaned to him by Wally Jabrowski. Anthony moved to stop them, but Krautzfeld accidentally vaporised him. Jennifer escaped and ran to Joe, but at this point Kreutzfeld couldn't care less. After seeing his son in the alternate dimension, he tried to follow him, despite Joe's protests but the door closed behind him, trapping him there forever.