Marcus Corvinus was the first Vampire, In an attempt to stop William Corvinus and all other Werewolves, Marcus approached Viktor, a dying warlord, to borrow his military genius and army in exchange for immortality. Viktor accepted and became one of the Vampire Elders. It is possible Marcus also personally infected Amelia adn they became the Vampire Elders. Death Dealers were Vampire warriors that were created to combat the growing spread of the Lycans.
David becomes a Vampire-Corvinus Strain Hybrid after Selene infects him with her blood to save his life due to a fatal attack by a Lycan, after he tries to protect her daughter. Later he aids her in defeating the Lycans controlling Antigen and rescuing her daughter Eve. It is like
Eve is the First Tri-Blood Hybrid, Her father is Michael Corvin, First Lycan/Vampire Hybrid, turned into Lycan by Lucian & then into Hybrid by Selena. Eve & Michael Corvin are from Corvinus Family and last desendants to Original Imortal Alexander Corvinus. Distant Grand Unles Marcus and Willaim Corvinus first Vampire & Werewolf. Her mother is Selene First Vampire-Corvinus Strain Hybrid, was given the blood of Alexander Corvinus to make her strong enough to stand against his son Marcus. She was raised by Vampire Elder Viktor and had trained under him. One of the last surving Death Dealers.
Vampire Elder Viktor was killed by Selena together with Michael when she was a Vampire. Michael has also killed William Corvinus First Werewolf. After becoming a hybrid, Selena has killed Marcus Corvinus & Quint Lane a Lycan-Corvinus Strain Hybrid. Eve's true power is yet to seen but is belived to be potentialy stornger than all. Making them the storngest Imortals with royal heritage of Immortals.
They could be leaders of their Coven of Imortals. All survivng Vampires surely would want strong new Leaders to survive against Lycans.