According to Oxford Biblical Studies, the patriarchs of the Old Testament were Abraham, Isaac and Jacob. Between them, these three men are figurative fathers of the Israelite nation.
Abraham was the father of Isaac. He and his wife Sarah were very old before they were finally able to conceive a child. According to Hebrew text, he was called by God to sacrifice his son, which was actually just a test of Abraham's devotion to God. Abraham's son Isaac was the father of Jacob, who bore the 12 sons who became the patriarchs of the 12 tribes of Israel. In addition to being key figures in Judaic literature, the Old Testament patriarchs are also key to Christian texts as their lineage continues on to eventually produce Jesus, who is the Christian Messiah.
Although both Jewish and Christian tradition accept the stories of Abraham, Isaac and Jacob as literal truths, there is some question as to whether these men historically existed. Some experts believe that the stories may have evolved from oral traditions that were common in the Mesopotamian Era around the time of their supposed existence. It is thought that in their current form, the stories of the Biblical patriarchs are only about 2,000 years old, 2,500 years after the events of the stories supposedly took place.