elephant becauase
The largest land animal on the planet, the African elephant, comes in as the toughest S.O.B. ever. This giant can fight off a pride of lions and has very little to fear from anything.
Elephants are extremely intelligent, which gives them the upper hand in most battles. They have enormous tusks that they can use to gore attackers and their trunks are mighty enough to smash an opponent flat. If worse comes to worst, the elephant can step on almost anything, crushing it to smithereens.
Occasionally a pride of lions will take down a sick, old or weak elephant, but that's very rare. If you don't believe me, just watch the video below. Anything that can fight off seven adult lions has to be the toughest animal in the world.