Marplon was a male inhabitant of Beta III in the 23rd century. As an an official, his duties included the absorption of new members. He was also one member of the underground that opposed the will of Landru. In 2267, when the USS Enterprise visited the planet and became trapped, he provided vital assistance to the landing party; he prevented Kirk and Spock from being absorbed, and he returned their weapons and communicators to them. After Reger collapsed emotionally, Marplon guided the landing party to the Hall of Audiences, so they could confront Landru. Marplon was played by Torin Thatcher.