Easy

Passed from father to son and shared between brothers, its importance is unquestioned though it is used more by others.

related riddles

What has black spots and a white face, is fat not thin, and helps you to win, but tumbles all over the place?

I am the yellow hem of the sea's blue skirt.

Though I should be unique, you've made most of us the same. I would be stronger, if my characters were stranger.