Who were Abraham and Isaac?

Answer 1

There were three patriarchs: Abraham, Isaac and Jacob. The book of Genesis (from ch.11 onward) centers around them.
Abraham (18th century BCE) came from ancestry that had been aware of God a couple of centuries earlier but had afterwards slipped into idolatry (Joshua 24:2). Nimrod, the idolatrous tyrant, had brought Abraham's father (Terah) from the Semitic ancestral seat near the conjunction of the Balikh and the Euphrates, and instated him in a position of power in his army in the royal Babylonian city of Ur, where Abraham was born. Nimrod persecuted any who would question his idolatrous cult.
The Kuzari (Rabbi Judah HaLevi, 1075-1141) states that Abraham was gifted with high intelligence; and, as Maimonides (1135-1204) describes, Abraham didn't blindly accept the ubiquitous idolatry. The whole populace had been duped, but the young Abraham contemplated the matter relentlessly, finally arriving at the conclusion that there is One God and that this should be taught to others as well. This is what is meant by his "calling out in the name of the Lord" (Genesis ch.12).

• Link: How did idolatry start?
  

While still in Ur, he remonstrated with passersby in public, demonstrating to them the falsehood of their idols; and our tradition tells how he was threatened and endangered by Nimrod.
Subsequently, Terah relocated to Harran; and it is here that Abraham began to develop a circle of disciples (Rashi commentary, on Genesis 12:5).

Later, God told Abraham in prophecy to move to the Holy Land, which is where Abraham raised his family.
He continued his contemplations, eventually arriving at the attitudes and forms of behavior which God later incorporated into the Torah given to Moses.

• Link: Thirteen basic Jewish beliefs
  

Abraham, with God's help, singlehandedly trounced the supremacy of the evil Nimrod.

He received God's promise of inheriting the Holy Land (Genesis 13).

He strove to raise a family (Genesis ch.15, 17, and 24) which would serve God (Genesis 18:19); and God eventually blessed his efforts, granting him many children (ibid., ch.16, 21 and 25), as He had promised (Genesis ch.17).

Abraham founded the Jewish people and lived to see his work live on in the persons of Isaac and Jacob; and he taught many other disciples as well (Talmud, Yoma 28b).

He saved the population of the south of Canaan from invading foreign kings (Genesis 14); and he was feared by neighboring kings (ibid., ch.12 and 20).

Abraham gave tithes (Genesis ch.14), entered into a covenant with God (Genesis ch.15 and 17), welcomed guests into his home (Genesis ch.18) unlike the inhospitable Sodomites (Genesis ch.19), prayed for people (Genesis ch.18), rebuked others when necessary (Genesis ch.20), eulogized and buried the deceased (Genesis ch.23), and fulfilled God's will unquestioningly (Genesis ch.22). He became renowned as a prince of God (Genesis 23:6).

All of these forms of behavior were based upon the ways of God, which Abraham comprehended through his contemplations. These, and similar personality traits, were the teachings of Abraham and his descendants (unlike idolatry, which had no moral character; with worship of the gods accompanied by things such as human sacrifice, "sacred" prostitution, and animal worship).

• Link: Pagan practices
  

It is therefore clear why God expresses His love for Abraham (Isaiah 41:8) and calls Himself the God of Abraham (Genesis 26:24), and says that Abraham obeyed Him fully (Genesis 26:5). And this is why Abraham is credited with having begun the religion which became known as Judaism. (However, Abraham and his descendants observed their traditions voluntarily, until the Giving of the Torah to Moses 3325 years ago, when God made it obligatory.)

Isaac is the second of the three Forefathers and (like Abraham and Jacob) one of the greatest personages in Judaism.
Isaac (Yitzhak) was a son of Abraham (Genesis ch.21); and God said that His covenant with Abraham would continue with Isaac (Genesis 17:18-19). Isaac had facial features that were identical to Abraham (Rashi commentary, Genesis 25:19).

God tested Abraham by asking him to offer Isaac as an offering (see Genesis ch.22); and this readiness for self-sacrifice bestowed a special holiness upon Isaac (Talmud, Yevamot 64).
Isaac married Rebecca (Genesis ch.24), his second cousin. Rebecca gave birth to two sons, Esau and Jacob (Genesis ch.25).

• Link: Rebecca
  

God spoke to Isaac, confirming His covenant with him (Genesis ch.26).
Despite harassment from the Philistines, Isaac enjoyed great success (ibid.). He reopened all the wells which his father had dug and the Philistines had stopped up (ibid.). The king of the Philistines, unable to ignore Isaac's phenomenal success, petitioned him to make a mutual treaty of non-aggression (ibid.).

In his advanced years, Isaac sought to bless his elder son Esau (Genesis ch.27). Rebecca took pains to thwart this and to ensure that Jacob would receive the blessing, since she had learned through prophecy (Genesis 25:23) that Jacob would be more favored by God.

• Link: Isaac's blessing
  

Later it became apparent that Isaac admitted to Rebecca's having done the right thing, since he blessed Jacob again (Genesis 28:1-4) even after he found out what had happened (see Genesis 27:6-16).

Isaac sent Jacob to the ancestral family seat in Mesopotamia to choose a wife (Genesis ch.28). Though Jacob didn't return for over twenty years (Genesis 31:38), God granted Isaac extra years, so that he lived on for two decades after Jacob's return.
Isaac was buried next to his father Abraham, in Hebron (Genesis 49:31).

Answer 2

Two key founders of Judaism. Abraham was Isaac's father.