In 2151, Koss' forthcoming wedding to T'Pol was postponed by T'Pol herself, so she could remain aboard Enterprise NX-01. By that point, Koss had met T'Pol only four times before. (ENT: "Breaking the Ice")
In 2154, after T'Pol returned to Vulcan following the Xindi incident, her mother, T'Les, urged her to marry Koss, but she still refused. Koss visited T'Pol and attempted to persuade her to marry him by offering to let her resume her career if she spent one year with him on Vulcan. He also offered to help her mother regain her position at the Vulcan Science Academy, from which T'Les had been dismissed because T'Pol had been involved in an incident at P'Jem. Under the condition of remaining on Enterprise for the time being, T'Pol finally agreed to Koss' proposal, and the two were subsequently married at T'Les' house. (ENT: "Home")
Later that year, Koss brought T'Pol an IDIC necklace from her mother, which contained a hidden map of Vulcan's Forge. After leaving Enterprise, he was contacted by the starship's commanding officer, Captain Jonathan Archer, who needed to reach the Vulcan High Command. For T'Pol's sake, Koss gave Archer and T'Pau his transporter codes, enabling them to reach the High Command and present the Kir'Shara there. He ended his marriage with T'Pol after the death of T'Les. Shortly thereafter, their marriage was officially dissolved. (ENT: "The Forge", "Kir'Shara", "Babel One")
Koss was played by Michael Reilly Burke.
In the writers' second draft script of "Breaking the Ice", this character's name was consistently spelt "Kos". In an ultimately discarded line of dialogue from the same script, T'Pol specified that Koss had been betrothed to her since they were fourteen years old.
In the script for "Home", Koss was initially described as "a striking Vulcan man approximately T'Pol's age." This would put his year of birth around 2088. After providing his name, the script went on to say, "Although tall and severe in appearance, we sense a total lack of pretension in this Vulcan."
Koss was present in an extended scene from "Home" (included in the ENT Season 4 Blu-ray). In the deleted portion of the scene, it was established that, prior to meeting Charles Tucker III, he had never before met a Human.