The lieutenant commander in charge of the USS Ariel, found by Kirk's landing party as a captive exhibit in the zoo of the highly advanced Lactrans.
Lieutenant Commander Tom Markel is the commanding officer of the Ariel, a small science vessel with a crew of six, in the Animated Series episode The Eye of the Beholder.
The Enterprise finds the Ariel abandoned in orbit of Lactra VII. Its log shows that the first three crew members to beam down stopped reporting, and that Markel then led the remaining two to the surface after them, leaving the ship empty in defiance of regulations.
Kirk, Spock and McCoy follow and are themselves collected by the Lactrans, huge slug-like beings of immense intelligence, and placed in a habitat with Markel and his surviving crew, Randi Bryce and the ailing Nancy Randolph. Markel explains that their captors regard humans as animals, and he works with Kirk on the plan that finally persuades the Lactrans to release them.