Almost nobody can pinpoint the exact history of the Rocket Shark, not unlike the human itself, only a lot more dangerous.
Dr. Karl Scholl, one of the most reknowned Rocket Shark experts, beleives that Rocket Sharks came into existence around '87 when Land Sharks were genetically morphed with J.A.T.O. (Jet-Feul Assisted Take Off) rockets. The government project that created them, was immeaditly aborted as the Sharks bred, then killed the remaining Land Sharks, making them extinct. Little is known, due to the fact that the Sharks killed the scientists who foolishly equiped them with diamond bladed chainsaws. Dr. Scholl analyzed the scrawling made in the scientists own blood in the lab of their demise.
Rocket Sharks today constanly patrol the planet, waitng for some reason to kill. Simple as that.