The first children of Adam and Eve, born after the Fall of Man. Once, when they were grown men, both Cain and Abel offered sacrifices to God. When Cain saw that Abel's pleased God whereas his did not, Cain murdered his brother out of jealousy. For his crime, Cain was exiled by God to a life of wandering in a distant land.
Note: God “set a mark upon Cain” to protect him in his wanderings. The “mark of Cain” now refers to an individual's or humankind's sinful nature.