The mechanical bull is a device used for fun by humans. This particular mechanical bull is a technologically advanced version, with added features to make riding it more fun. Features like flame breath, country music, and a pathological hatred of the color red.
The mechanical bull was sent over from the mainland to Griffin Rock for testing, and ended up being installed in the Griffin Rock Fun Zone. It didn't stay there for long, busting a hole through the wall and going on a rampage through town, which was only brought to a halt by the rescue team. Disabled, the bull was taken to the laboratory, where Doc Greene deemed it too big and dangerous for the Best Left Forgotten room. In the process of tagging it to be transported to the Island of Misfit Tech, the bull was accidentally reactivated, and it took Cody with it through the Beam Box. Reaching the island, it immediately ran off with Cody's jacket. He later found the bull again, and discovered that it was made docile by the color blue, which he'd inadvertently been painted by a rogue paint cannon. Cody was able to use this to his advantage, marking Heatwave blue with the cannon and using the bull to destroy some red metal-eating bugs. The bull was returned to Griffin Rock where it was used to destroy a prototype Scrapmaster, and Cody successfully convinced Chief Burns and Doc Greene to keep the bull in town.