Abel was one of the direct descendants of the First Civilization, through his parents being Human-First Civilization hybrids themselves. At one point during his life, he obtained an Apple of Eden, and was killed by his older brother, who wanted the artifact for himself.
Abel is considered to be the first murder victim in recorded human history, while Cain was the first recorded murderer. Cain was subsequently branded with a mark for his deed, which was later adopted by the Children of Cain as their insignia. The Children of Cain would go on to be known centuries later as the Knights Templar.