Relativity teaches us nothing about animals or their qualities. It teaches about the speed of light. You mean: What is proportionally the strongest animal in the word? I think it's the ant. But I am not sure.

What is the world's strongest animal? it is also one of the fastest and the smallest that exist today. "Copepods" are a species of crustaceans maxilópodos very small, about 1 mm, which are abundant in freshwater and saltwater.

Hippopotamus

The Hercules Beetle. Absolutely it is weaker than any other mammal of course ,but relatively to its body weight and upon calculations it is the strongest! ( or one of the strongest).