Abel
Abel is one of the two sons of Adam and Eve. His brother (Cain) killed him for simply being jealous.
Abel married one of his sisters. Cain married the other. (The two girls were twins)
In Christianity, Comparisons are sometimes made between the death of Abel and that of Jesus, the former thus seen as being the first martyr: in Matthew 23:35, Jesus speaks of Abel as righteous; and the Epistle to the Hebrews states that The blood of sprinkling ... [speaks] better things than that of Abel (Hebrews 12:24). The blood of Jesus is interpreted as bringing mercy; but that of Abel as demanding vengeance (hence the curse and mark).
Abel is invoked in the litany for the dying in Roman Catholic Church, and his sacrifice is mentioned in the Canon of the Mass with those of Abraham and Melchisedek. The Coptic Church commemorates him with a feast day on December 28.
In classical times, as well as more recently, Abel was regarded as the first innocent victim of the power of evil, and hence the first martyr.