Experiment 155 was the 155th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to make different kinds of burgers.
155 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 Burger.
Burger is a yellow Spongebob Squarepants-like experiment eating a burger.