Two (The Ark)

Two was the second-in command of the Monoids, during and after their revolution against the humans on the Ark.

Two's name was based on rank; he was second only to One. His communicator had the number 2 written on it, an indication of this rank. Two scouted Refusis II ahead of the main Monoid party. A Refusian used force to prevent him breaking objects in a rage.

Two reported back to the Ark and was about to tell them about the Refusians when a Refusian killed him by having his landing craft explode. (TV: The Ark)

Behind the scenes
Of the Monoid actors (Edmund Coulter, Frank George, Ralph Carrigan, John Caesar), it is never made clear who played which Monoid.