In the
Bible, the Book of
Genesis,
God was angry at
Adam and Eve's son
Cain for killing Cain's brother
Abel.
As punishment, God put a curse on him. No food would grow out of the ground for him, and he was to be banished. God put a mark upon him, so nobody or nothing would harm him, or risk wrath from God ten times worse. According to the Bible, he eventually wandered alone to the land of Nod, or Wandering.
Throughout time, there have been religions that have tried to guess what happened to him, many assume he went and started his own race of people. Originally the Mormons believed that black skin was the Mark. (see Mormonism and Racism)