In the Bible, he's the third son born to Adam & Eve
[DOC] [TLE] Genesis 4:25 Adam made love to his wife again, and she gave birth ... [PAR] She named him Seth, for she said, "God has granted me another son in ... And 
Adam knew his wife again, and she bore a son and called his name ... NET Bible 
And Adam had marital relations with his wife again, and she gave birth to a son.