Isaac is the second son of Abraham, a half brother to Ishmael, and the divinely promised firstborn son of Abraham and Sarah (Genesis16, 19) with whom God establishes the covenant first granted to Abraham (Genesis19, 21; 21:12; 26:2-5).  "Isaac" means "he laughs," and on several occasions he is associated with laughter.  For example, Abraham laughs when God tells him that he and Sarah will have a son (Isaac), because Sarah is 90 years old at the time (Genesis17).  Likewise, Sarah laughs when she hears the divine promise of a son (Genesis12).  In a less familiar association, Sarah banishes Ishmael and his mother, Hagar, because he was, in literal Hebrew, "isaacing," which is usually translated into English as "mocking" or "playing" (Genesis 9).  It is hard to say what Ishmael was doing exactly, but Sarah seems to have taken it to be a way of "making fun" of Isaac.  

Isaac may best be known for his role in God's testing of Abraham (Genesis 22).  God commands Abraham to take Isaac, his only beloved son, and sacrifice him.  Because Abraham proves he is willing to do so, a ram is provided at the last minute as a substitute for Isaac upon the altar.  

Later, Isaac marries Rebekah and they have twin sons, Esau and Jacob.  Esau, the outdoorsman, is Isaac's favorite son; but, Isaac is tricked into pronouncing his final blessing upon Jacob, the younger of the two (Genesis 27).  Genesis 26 relates several stories about Isaac.  In one instance, Isaac attempts to trick King Abimelech of Gerar into believing that Rebekah is his sister instead of his wife.  Because of this, he falls out of favor with Abimelech and the Philistines.  According to Genesis 35:28, Isaac dies at the age of 180 years.

Throughout these stories in Genesis, Isaac is portrayed as a rather passive character, especially when compared to Abraham his father, Rebekah his wife, and Jacob his son.  He is obliging to Abraham (Genesis 22), consoled by Rebekah (Genesis 24:67 – throughout this story Isaac plays virtually no active role, and verse 67 uses a passive verb to end the story on a passive note) and duped by Jacob (Genesis 25). Even in Genesis 26, he repeats previous actions of his father.

Nonetheless, the name Isaac is routinely invoked throughout the Old Testament in the phrase, "the God of Abraham, Isaac and Jacob/Israel," because he, like his father and his son, is an heir to the divine covenant.  In the New Testament, he is included in the genealogy of Jesus (Matthew 1:2; Luke 3:34), and he is mentioned by the writer of Hebrews as a person of faith (Hebrews 11:20).  

During the first several centuries of the Christian Church, Isaac was interpreted as a Christ figure, especially because in Genesis 22, he—the innocent, beloved son—bears his own wood for his sacrifice (Genesis 22:6).  Rabbinic Jewish tradition views Isaac in similar fashion.  Taking him to be of adult age in Genesis 22, and therefore conscious of his sacrifice, Isaac becomes a model for later Jewish martyrs.