Experiment 253 was the 253rd genetic experiment created by Jumba with Hämsterviel's funding. He was designed to undue the ability of 252.
253 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai.
At the unknown point, he was activated, captured, tamed and named Uncrete.