We don't know too much about Abraham. But one thing we do know is super essential: he created that VIB (Very Important Book) the Codex, also known as the book of Abraham the Mage. We also know that Abraham had the gift of Sight, and prophesied that there would come a day when his book and all the knowledge it contained would be needed. Only humans can touch his book, as Hekate tells us: "it was Abraham's ultimate joke. He married one of the first humani, and I believe he wanted to ensure that only his children could handle the book" (14.27).
Frankly, we don't mind that we know so little about Abraham because even Nicholas Flamel doesn't know what Abraham was—whether he was a human, one of the Elder Race, or "something else" (14.38).