Cain was the son of Eva and Cano, a man of the Nodite race; he had a natural bellicose inheritance.  He was born before the Adamic caravan reached the second garden.  He was two years older than Abel, who was the first son of Adam and Eve in the second garden. Cain chose to dedicate himself to agriculture.  He had always defied family discipline and despised Adam's religion.  He slew Abel.  Because of that act he finally repented and was inhabited by an Adjuster.  Adam and Eve encouraged him to leave the second garden.  He went to the land of Nod for a wife.  He married Remona; his first son was Enoch. 
The expression avenged seven times was applied to Cain, because his tribal mark was considered to be that of the tribe that would take revenge up to seven times on whoever killed him.  The tribal mark was vital in the days of Cain, as it ensured that someone could survive. 
See also: UB 76:2.