Weyoun was a Vorta diplomat and leader in the service of the Dominion during the late 24th century. Like all Vorta, he was a clone; at least eight copies (five of which were encountered by the Federation) were known to exist. Weyoun became a well-known Vorta in the Alpha Quadrant during the Dominion War, serving as the Dominion representative to the Cardassian Union. In this capacity, he personally oversaw most aspects of the war, although his presence was largely to ensure the loyalty of Cardassian leaders such as Gul Dukat and later Legate Damar.

The war brought Weyoun into contact with many leaders from the Alpha Quadrant. He visited Deep Space 9 to negotiate with Benjamin Sisko when the cold war between the Federation and Dominion showed signs of eroding into open hostilities. Shortly thereafter, he returned with a fleet of Cardassian and Dominion warships to take control of the station, and went on to serve as the Dominion overseer of the station during the brief occupation that followed. In this capacity, he personally negotiated a nonaggression pact with Bajor and dealt with representatives from such powers as the Romulan Star Empire, Breen Confederacy, and Tholian Assembly. Until his death, he remained the only "Solid" that the Female Changeling claimed that she had ever trusted.

Weyoun 4 was encountered by the Federation in 2372 as the supervisor of a Jem'Hadar attack ship and its crew of Jem'Hadar, led by Omet'iklan. After his ship was attacked by a group of renegade Jem'Hadar, Weyoun chose to recruit the assistance of Captain Sisko in quelling the rebellion. Weyoun withheld crucial information from Omet'iklan about the rebels' fortress: an Iconian gateway on Vandros IV. However, the Jem'Hadar under Weyoun's supervision remained loyal to the Founders and successfully completed the mission of eradicating the Jem'Hadar rebellion. Following the battle, Omet'iklan killed Weyoun for questioning his loyalty to the Dominion.

(DS9: "To the Death")

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