Board Thread:Naruto Discussions/@comment-4704473-20140625072535/@comment-5407586-20140626135235

Kaguya had the ultimate chakra, along with Byakugan and Rinnegan/Sharingan. Hagoromo and Hamura, her sons, split up that power, with the first inheriting the Rinnegan and the second the Byakugan. Hagoromo's sons, Indra and Asura, inherited their father's "eyes" (the Sharingan) and "body" (life force). That's all there is to it.