Rust, A.K.A. Experiment 537, is an illegal genetic experiment created by Jumba Jookiba. He is designed to cause oxidization on any metal (does so by blowing bubbles causing any metal surface they come into contact with to instantly become covered in rust).
Experiment 537 was the 537th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to cause oxidization on any metal.
537 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 Rust.
Was reprogrammed so that it would get rid of rust instead of create it.