Cain

Legend tells that Cain was the first human being that murdered. He was envious of his brother and in his rage clubbed him to death. Artifacts found in a cave below a Nod facility indicate a link between the Brotherhood and this legend. Whether Nod really is thousands of years old or they just named themselves after the 'Land of Nod' which Cain was banned to after the murder is unknown. Some even believe Cain and Kane are identical. Hence he must be immortal which would explain why Kane could survive the Ion Cannon strike on his temple in Sarajevo.