Jacob and his brother Esau were born to Isaac and Rebekah
When they grew up Jacob, with help from his mother, disguised himself as Esau and tricked his father Isaac into blessing him. At that time people believed that if a father blessed his son that son would become the leader of the family after his father's death. Furthermore he would inherit a double portion of his father's property. They also believed that once a blessing was given it could not be withdrawn. A blessing was legally binding.