|Father:||James T. Kirk|
- Occurs in an alternate mirror universe:
After Commander-in-Chief Spock was overthrown by the Imperial Starfleet, Marcus led a resistance movement dedicated to carrying on Spock's vision of reform, but his activities unfortunately helped fuel the rise of the Klingon-Cardassian Alliance and its subsequent conquest of Earth. Beset by guilt over his role in this, Marcus took his own life.
- In another timeline Marcus was killed trying to free scientists from a prison planet.