As I recall, Cain was the one of the sons of Adam and Eve. He killed his brother because he felt that God liked his brother's animal sacrifices better than his veggies and fruits. And then, after killing him, God asked him,
New International Version (©1984)
. . . . "Where is your brother Abel?" "I don't know," he replied. "Am I my brother's keeper?"
http://bible.cc/genesis/4-9.htmThe rest of that part of the story of creation
11 And now
thou cursed from the earth, which hath opened her mouth to receive thy brother's blood from thy hand;
12 When thou tillest the ground, it shall not henceforth yield unto thee her strength; a fugitive and a vagabond shalt thou be in the earth.
13 And Cain said unto the LORD, My punishment greater than I can bear.
14 Behold, thou hast driven me out this day from the face of the earth; and from thy face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass, every one that findeth me shall slay me.
15 And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him.
16 And Cain went out from the presence of the LORD, and dwelt in the land of Nod, on the east of Eden.
http://www.kingjamesbibleonline.org/Genesis-Chapter-4/
Vegans, take note. God favors carnivores according to the Bible. (Just joking. Love my veggies.)