Vreenak enjoyed drinking the Romulan beverage kali-fal. When offered a Starfleet-replicated drink in 2374, he noted it was, "lacking in aroma", and should, "forcibly open one's sinuses well before the first sip." (DS9: "In the Pale Moonlight")
Vreenak rose to the position of senator in the year 2360, later becoming Vice-Chairman of the Tal Shiar, secretary of the War Plans Council, and one of Proconsul Neral's most trusted advisers. In 2371, Vreenak was nominated by the Romulan Senate Council for the prestigious Praetor Colius Award, becoming the youngest nominee ever.
Two years later, he was responsible for negotiating the non-aggression pact between the Romulan Star Empire and the Dominion. One of the most ardently pro-Dominion senators, Vreenak had very little faith in the Federation-Klingon Alliance's chances during the Dominion War.
In 2374, Vreenak attended a high-level diplomatic meeting with the Vorta official Weyoun, on the planet Soukara. During his return journey, Starfleet Captain Benjamin Sisko convinced him to make a secret detour to Deep Space 9, in order to view supposed evidence of a planned Dominion invasion of Romulan space. In reality, Sisko had obtained a optolythic data rod which he had then used to forge a holographic record of a secret meeting showing Weyoun and Legate Damar discussing the invasion. It was Sisko's hope that Vreenak would return to Romulus and convince the Senate to join the war against the Dominion.
Upon examination of the data rod, Vreenak discovered that the evidence was forged, and headed back to Romulus threatening to expose the plot. However, due to sabotage by Elim Garak, Vreenak's shuttle exploded while en route, killing the senator, and at least two of his guards. The subsequent investigation by the Tal Shiar uncovered the fabricated evidence, but its defects appeared to be the result of the explosion. The Romulans logically concluded that the Dominion had assassinated Vreenak to prevent him from returning to Romulus with the evidence, and joined the Dominion War on the side of the Federation Alliance. Both Garak and Sisko (who knew for sure that Garak killed him and, before, tacitly gave him the suggestion) shared the guilt of his death to a greater good. (DS9: "In the Pale Moonlight")
Memorable quotes Edit
"So you're the commander of Deep Space 9. And the Emissary of the Prophets. Decorated combat officer, widower, father, mentor, and... oh, yes, the man who started the war with the Dominion. Somehow I thought you'd be taller..."
"Sorry to disappoint you."
"To be honest, my opinion of Starfleet officers is so low that you'd have to work very hard indeed to disappoint me."
- - Vreenak and Benjamin Sisko
" I look forward to seeing your station, while it's still here, that is. The way the war's going with the Federation, it may not be around much longer."
- - Vreenak, to Benjamin Sisko
"You are persistent, captain, I'll grant you that. But dogged determination isn't enough to change the reality of your situation. Time is definitely not on your side. The Dominion shipyards are working at one hundred percent capacity, yours are still being rebuilt. The Dominion is breeding legions of Jem'Hadar soldiers every day; you're experiencing a manpower shortage. But most important, the Dominion is resolved to win the war, at any cost."
- - Vreenak
Senator Vreenak was played by actor Stephen McHattie.
The script for "In the Pale Moonlight" gives the pronunciation of Vreenak's name as, "VREE-neck". Of his introductory scene, it describes him as being, "a little bemused by this whole adventure and we get the feeling it may be hard for him to take Sisko seriously." 
Shortly after the episode aired in 1998, the line "It's a faaaaake!" as delivered by McHattie, became a popular internet meme, with fans using the term as a common reply in Usenet and forum discussions. As the years went on, the scene became further popularized through animated GIFs and other spoof images and videos.      
Vreenak is mentioned in a number of apocryphal works.
The Star Trek: The Lost Era novel Serpents Among the Ruins gives his first name as "Merken", and indicates he was in public service around 2311, the year of the Tomed Incident. He is shown as one of the senior aides to the Romulan ambassador during negotiations leading to the Treaty of Algeron, and is a staunch Romulan nationalist and supporter of the novel's antagonist, Admiral Vokar.
Vreenak is also mentioned in the Tales of the Dominion War short story "Blood Sacrifice", which takes place immediately before and during the events of "In the Pale Moonlight". During a conversation between Ambassador Spock, Kimara Cretak and two of the story's characters, Ruanek and Amarik, Amarik tells the others of Vreenak's death.
The Pocket DS9 novel Hollow Men bridges the gap between "In the Pale Moonlight" and "His Way", with Sisko and Garak traveling to Earth to take part in Allied talks between the Federation, the Romulans and the Klingons. During their visit, Sisko informs Starfleet of the extent to which he and Elim Garak were involved in the death of Senator Vreenak.
In an alternate universe as established in the Star Trek: Myriad Universes novel A Gutted World, Starfleet considers Senator Vreenak to be one of several high ranking Romulan officials to have been replaced by Changelings.