Marcus II was the inhabited second planet of its star system. This planet was the homeworld of the noted artist Sten. (TOS: "Requiem for Methuselah")

According to the section on the system in the "Star System Data" appendix of the "Introduction To Navigation" booklet included with the first published volume of Star Trek Maps, the Marcusites never developed space flight, instead fighting a series of devastating nuclear wars. Theirs was described as being, by the late 2260s, a dwindling population that had become noted mainly for its artistic achievements, including those of Sten.