He had a strange birth. His mother, a cow, ate some magic grass which turned out to be full of maleness. She became pregnant and soon gave birth to this fully-formed Nature God. It’s not everyone who can claim their father is a tuft of grass.
A great shape-changer himself, he became involved in animal evolution and did his bit for conservation by putting each species in its most suitable habitat — taking fish out of the desert, persuading lions to stop nesting in trees, and so on. He could certainly tell Charles Darwin a thing or two about survival of the fittest.
Oddly enough, humans are his favorite animal. He gave us lots of freedom to run wild, trample all over the planet and basically do our own thing. No wonder all the other animals hate us.
HEITSI-EIBIB is also something of a folk hero, having sorted out GA-GORIB, a nasty taunting demon who used a large pit to trap and devour animals. When our hero fell into the pit, he quickly evolved into we don’t know what and emerged licking his lips. The demon was never seen again.
Nowadays HEITSI-EIBIB potters around in graves and caves. He’s probably taking care of the critically endangered squib-nosed fishbat or something. Don’t worry, he can still be approached if you need good luck in hunting. You can’t lose with the God of Natural Selection on your side.