Because not all animals live in the same areas, there are different food chains to include the different animals in those different areas. Therefore, there isn't just one animal atop "the" food chain. There are apex predators, meaning they predate on other animals but don't fall prey to other animals themselves unless injured, ailing, old, weak or undergoing some unusual circumstances. They are at the top of the food chain where they live. Some examples are bears, crocodilian, wolves, hyenas, big cats, and so on.