Colonel Grat was a Tandaran military officer in charge of Detention Complex 26, a prison on a moon in Tandaran space, where dozens of innocent Suliban were held during the Tandarans' conflict with the Cabal.
In 2152, a shuttlepod carrying Enterprise officers Captain Jonathan Archer and Ensign Travis Mayweather was shot down by Tandaran ships when they accidentally entered the moon's military zone. They were detained and questioned by Grat, and although he believed they were not affiliated with the Suliban, he could not release them, citing strict regulations preventing him from doing so.
Grat told the two Starfleet officers that they could appeal to the Central Magistrate's Office for their release before Grat could let them go, and that they were not permitted to contact Enterprise. He stated that a transport would arrive to take them to Tandar Prime in three days, but until then, they could not leave or communicate outside the detention complex.
Later, Grat contacted Enterprise using an untraceable triaxilating channel and informed the crew of the situation. He also told them they could not speak with the imprisoned officers, but sent the ship coordinates for Tandar Prime so that they could attend the hearing of their crewmates.
Having learned from Archer that Enterprise had prior encounters with the Suliban Cabal, Grat took it upon himself to contact Tandaran intelligence, who relayed to him information regarding the events surrounding the Broken Bow Incident, including news that the Cabal had made attempts to capture a Klingon named Klaang, and that Archer had had contact with a former Cabal member named Sarin as well as having had an encounter with Silik. Believing Archer had valuable information on the Cabal and who they were working for, Grat brought the captain in for questioning. The captain refused to be interrogated, however, and instead asked why the Tandarans had detained Suliban who were not members of the Cabal.
Grat claimed the Suliban were imprisoned for their own protection, to prevent them from becoming innocent casualties of war and to ensure they could not be recruited into the Cabal. Grat then persisted in questioning Archer for further information on the Cabal and his involvement in the Temporal Cold War. When Archer stood his ground, Grat threatened him with a longer stay in the detention complex.
Grat later contacted Enterprise to inform the officers aboard the ship that their crewmates' hearing had been "postponed." This time, however, Communications Officer Hoshi Sato was able to isolate Grat's frequency and T'Pol ordered Enterprise to proceed to the location of the detention complex.
When Enterprise assumed orbit around the moon, Grat threatened the vessel's crew. However, he could not prevent Archer and Mayweather finally escaping, along with the detained Suliban, of whom there were eighty-nine individuals. Stealing a Tandaran pistol from Grat, Archer locked him in the facility's isolation cell. (ENT: "Detained")
Later that year, while vacationing on planet Risa, Archer suspected that a disguised Tandaran named Keyla was an agent of Colonel Grat sent to retrieve information from Archer. Keyla denied the accusations, claiming she had never even heard of Grat. Before Archer could question her further, she knocked him unconscious and escaped. (ENT: "Two Days and Two Nights")
In the final draft script of "Detained", Grat was described as being "in his 50's." The teleplay went on to comment, "He's an affable, cultured man who also harbors deep resentment toward the Suliban." Rather than Grat being locked in a cell at the end of the story, the script featured him ultimately hatching a plan to take Archer, in Grat's shuttle, to Tandar Prime and question him there though then being cold-cocked by Reed, with Grat's own Tandaran pistol.
The role of Grat, which was not especially written for Dean Stockwell, was prompted by Scott Bakula and the producers of Star Trek: Enterprise agreeing that having Stockwell in their series would be a good idea. Said series co-creator and Executive Producer Rick Berman, "When an appropriate role came along we contacted Dean, and he was delighted to do it." (Star Trek: Communicator issue 138, p. 20)
Dean Stockwell struggled with some of Grat's dialogue. One week after "Detained" wrapped production, Scott Bakula commented, "He got stuck with having to recap a lot of history from the first season, in particular about the Suliban, and he was like: 'You have the Suliban, and he's a Tandaran.' It was so great, but he looked at me like, 'What am I talking about? What is this all about? So you have Suliban, Tandaran, Barathan, Pilgrims?' and he didn't know which end was up!" (Star Trek: Communicator issue 138, p. 85)
The portrayal of Grat thrilled Brannon Braga, who created Star Trek: Enterprise together with Rick Berman and also served as an executive producer on the series. Braga enthused, "Dean did an amazing job." (Star Trek: Communicator issue 139, p. 27)