(covers information from several alternate timelines)
Vosk was perceived as being the most dangerous participant in the Temporal Cold War by Daniels' faction, and he was once very nearly captured by them. However, Vosk developed a form of stealth time travel, allowing the Na'kuhl to escape to Earth in the year 1944 in a timeline which had been severely altered by multiple temporal incursions by various Cold War factions. In this timeline, the Nazis had launched a successful invasion of the United States East Coast and were steadily moving forward in their efforts to conquer the world. Vosk formed an alliance with the Nazis, promising to provide them with highly-advanced technology with which to wage their war in exchange for materials and resources with which to build a temporal conduit to return to the future.
Vosk, while working with the Nazis, held the rank of obersturmbannführer. He was often at odds with the German Army's generalmajor that served as the liaison between Adolf Hitler and Vosk's people, and who grew impatient at Vosk's stalling. (ENT: "Storm Front") When Vosk and his people were preparing to return to their own time, the treacherous Na'kuhl leader ended his alliance with the Nazis by killing the generalmajor. (ENT: "Storm Front, Part II")
In one possible timeline, Na'kuhl eventually completed the conduit and used it to launch an attack on Daniels' faction, igniting the Cold War into an all out conflict and resulting in the very alternate timeline to which they had escaped.
In a last-ditch effort to restore the timeline, Daniels transported Captain Archer and Enterprise NX-01 from 2154 to 1944 so they could stop Vosk, when he was most vulnerable. The crew of Enterprise was eventually successful, destroying the temporal conduit moments before Vosk could enter it. This had the effect of resetting the timeline and bringing the Temporal Cold War to an end. (ENT: "Storm Front, Part II")
Vosk was played by Jack Gwaltney.
In the final draft script of "Storm Front", Vosk was initially referred to as "an alien belonging to the same race as the being we saw at the end of 'Zero Hour'" and the script went on to describe him thus; "Vosk exudes frightening intelligence and a calm, calculated authority." The script also mentioned that Vosk would be costumed in a Nazi officer's uniform.
In an ultimately omitted line of dialogue from the final draft script of "Storm Front", Vosk assured the German Nazis, while visiting the White House, "Your concerns are understandable, gentlemen… but unfounded. The world will be yours… and the future will belong to us all."
Vosk appears in the Star Trek Online mission "Temporal Front". He holds the rank of general and commands a fleet of ships intending to travel into the past via a portal; he sends an operative to 2410, the game's present day, to attempt to assassinate the Federation President and the Klingon Chancellor during a peace summit. After thwarting the assassin, the player character travels with Captain Benjamin Walker of the Wells-class timeship USS Pastak to the 29th century to apprehend Vosk, but he escapes by traveling through the portal. As the player and Captain Walker scan the timelines to search for Vosk, they discover his fate at the hands of Jonathan Archer in 1944.