Cain קין
Adam's eldest son, a farmer, the first murderer
Kayin is the first person born in the ordinary way and the first to bring an offering by his own initiative. He is a farmer; his brother Hevel is a shepherd. Kayin brings «from the fruit of the ground» — the text does not say «from the best», and the sages hear everything in that silence.
When his offering is not accepted, God warns him: «Sin crouches at the door, but you can rule over it» — the Torah's first statement of free will. Kayin does not listen. In the field he kills his brother, and answers the question «where is Hevel your brother?» with the line that became proverbial: «Am I my brother's keeper?»
His sentence is exile rather than death, and a protective mark. He builds the first city and names it for his son Chanoch; from his line come herding, music and metalwork. Midrash says he was killed by his descendant Lemech.