We Jews speak casually of Abraham being a Jew, because he received the covenant from God. But of course we know that to be technically inaccurate. He is, rather, the Patriarch of the Jewish people. He was actually a Sumerian who because a Hebrew.
The Jews, or People of Israel, actually originated with Abraham's grandson, Jacob (renamed Israel) and his 12 sons, who founded the 12 tribes of Israel. Later in history, three of these tribes (Judah, Benjamin, and Levi) along with a smattering of refugees from the others went into captivity in Babylon where they were called Jews as a group. Today we are still called Jews, although among ourselves we still call ourselves B'nei Yisrael, the Children of Israel.