Talok was a long-term, deep-cover Romulan operative who posed as a Vulcan military officer in the 22nd century. In that capacity, he served under T'Pol during the Tomed mission, and secretly attempted to further the efforts of the Romulan Star Empire to conquer Vulcan.
Talok had entered into a covert alliance with Administrator V'Las, the head of the Vulcan High Command, to facilitate what Talok referred to as the "reunification" of the Vulcan and Romulan peoples. In 2154, Talok, who held the rank of major on Vulcan, embarked on a mission to retrieve the Kir'Shara, the record of Surak's original teachings. As the revelation of Surak's true philosophy would seriously undermine V'Las's authority, thereby eliminating the Romulans' control of the Vulcan government, this mission was considered to be of the utmost importance. However, Talok ultimately failed in stopping Starfleet captain Jonathan Archer from presenting the Kir'Shara to the High Command, leading to the relief of V'Las as Administrator, and the dissolution of the High Command.
In response to these events, Talok was forced to return to Romulus, as his position had become compromised. Prior to Talok's departure, V'Las confronted Talok, accusing him of failing in his mission to preserve Romulan influence on Vulcan. Refusing to take V'Las with him, as V'Las's disappearance at the same time V'Las was being investigated would cause too much suspicion, Talok reassured V'Las that recent events were only "a minor delay," and that reunification was "only a matter of time." (ENT: "Kir'Shara")
Talok was played by actor Todd Stashwick.
In the final draft script of "Kir'Shara", Talok was described thus; "Two meters tall, he's a powerful figure."
In the original draft of "Kir'Shara", Major Talok was a native Vulcan and was not an undercover Romulan operative. Originally, the Romulan spy in the final scene was to have been a new, never-before-seen character, but there was no money left in the budget to pay for another speaking role. Writer Mike Sussman adjusted the scene, turning Talok into the Romulan spy, as the major's role had already been budgeted for.
The re-use of a Romulan uniform from Star Trek Nemesis helped trim the budget further, allowing the scene to be included in the finished episode. Had the scene been cut, as it very nearly was, the Romulans' role in the political strife on Vulcan would have remained completely hidden, even from the audience. (Information provided by Mike Sussman.)