Raised on Arisia colony, which was plundered by EarthGov, Marcus was drafted into Earthforce just prior to the end of the Earth-Minbari War. Afterwards joined the Anla'Shok (the Minbari Rangers) in honour of his brother, who was killed in a Shadow attack (Matters of Honor, Learning Curve, and the novel To Dream in the City of Sorrows).
He arrived on Babylon 5 when his training camp, the Drazi colony of Zagros 4, was attacked by Shadows (Matters of Honor), and has since then worked with the crew and been a secret admirer of Susan Ivanova - willing to lose his virginity to her (The Summoning) - although she has shown no signs of reciprocating his feelings (Exogenesis). Could this be the deep, dark secret he is unwilling to share (Ceremonies of Light and Dark)?
He accompanied Franklin on his first reconnaissance mission to Mars (Racing Mars, Lines of Communication) and knows the complete lyrics to Gilbert and Sullivan's Pirates of Penzance, to Franklin's annoyance (Atonement).
Played by Jason Carter, who has also appeared in Third Rock From the Sun, Lois & Clark: The New Adventures of Superman, Charmed, Viper, and Beverly Hills 90210.