Dolphin

Dolphins play an important role in keeping their environment in balance. They eat other animals – mainly fish and squid – and are themselves a source of food for some sharks and other creatures. Without dolphins, the animals they prey on would increase in number, and their predators wouldn't have as much to eat. Dolphins are extraordinarily intelligent animals who also display culture, something which was long believed to be unique to humans (although now recognized in various species). 

Dolphins are altruistic animals. They are known to stay and help injured individuals, even helping them to the surface to breathe.