The Crocodile has the most powerful bite on the planet, but you can keep their jaws closed with just some duct tape.
A crocodile's bite is approximately 5,000 psi (pounds per square inch). In layman's terms, that's about 15 times the biting strength of a rottweiler, and more than 12 times the strength of a great white shark.
Crocodiles bite pretty hard, but their ancestors were much, much worse. The 40-foot-long, 17,000 lb, prehistoric "SuperCroc" could bite down on its prey with a force of 18,000 psi. To get an idea of what it feels like to get crushed by SuperCroc's 6-foot jaws: imagine tying a Mack Truck to your waist, and letting the truck roll off the top of a building.
While the crocodile has the strongest bite in the planet, that still doesn't protect it from getting pwned by a leopard, as evidenced by the picture.
(sources: 1, 2, 3, 4)