Marooned and Captured
In early 2374, Keevan and his unit of Jem'Hadar crashed on a class M planetoid within a dark matter nebula in Cardassian space. With his ship destroyed and only a handful of vials of ketracel-white remaining, Keevan was forced to ration it among the ten Jem'Hadar who survived. To make matters worse, Keevan himself received serious injuries in the collision and the unit's communications equipment was heavily damaged, leaving them unable to submit a distress call.
Fortunately for Keevan another Jem'Hadar attack ship, containing Captain Benjamin Sisko and his crew on a secret mission to infiltrate Dominion space, also crashed on the planet just a few days later. The Jem'Hadar in Keevan's unit were able to successfully capture Ensign Nog and Elim Garak from the ship, whom Keevan then ordered to be traded for the services of a Starfleet doctor to treat his injuries.
Following his orders, Third Remata'Klan organized a meeting with Captain Sisko and the exchange was carried out, with Doctor Julian Bashir returning to the Jem'Hadar camp, where he successfully healed Keevan.
After recovering from Bashir's treatment, Keevan knew that once the ketracel-white had run out, the Jem'Hadar would turn on him and each other. Realizing this, he offered Captain Sisko a trade; he would order his Jem'Hadar to attack the Starfleet camp but would reveal the attack plan to Sisko beforehand, allowing the Starfleet crew to eliminate the Jem'Hadar with ease. In return, Keevan would surrender to Sisko and escape death by becoming a prisoner of war. When Keevan presented himself for surrender, he was smug and emotionally cold towards the events that had happened promoting Captain Sisko to be visibly disgusted as he ordered Keevan to be restrained while ordering other crew members to form a burial detail.
Though Sisko was reluctant to accept the plan at first, when Keevan informed him the Jem'Hadar would be attacking his camp regardless, Sisko had no choice but to relent. In the ensuing firefight, all of Keevan's unit were swiftly killed at the cost of one Starfleet officer, Ensign Gordon.
Following the battle, Keevan surrendered himself and the Jem'Hadar communications device to Captain Sisko, resulting in his escape from the planet and subsequent imprisonment by Starfleet. (DS9: "Rocks and Shoals")
Prisoner Exchange and Death
Later that year, Keevan was used as part of a bargain for a prisoner exchange between the Ferengi Alliance and the Dominion. Following the capture of Quark's mother Ishka, Major Kira Nerys convinced Starfleet to allow Quark to trade Keevan in exchange for his mother's freedom, in return for saving her from incarceration during the occupation of Deep Space 9 months earlier.
Keevan, for his part, took no pleasure in the idea of being returned to the Dominion. As a Vorta field supervisor, he had been expected to commit suicide to prevent capture. Having failed to do so, he fully expected "a most unpleasant debriefing", followed by an execution.
Quark, along with his team of Ferengi, transported a handcuffed Keevan to the abandoned Cardassian space station Empok Nor where the exchange was to take place. While on the station, Quark's cousin Gaila took first watch over Keevan but soon fell asleep, giving Keevan an opportunity to escape. Though he managed to make it to their ship, Quark had earlier told his brother Rom disable the impulse engines, thereby preventing Keevan from departing.
Keevan was discovered by Quark and eventually led back to the station's infirmary in time for the exchange. However, during a heated argument between Quark and Gaila, Gaila accidentally shot and killed Keevan before the transfer could happen, necessitating another plan of action.
Growing desperate, Nog engineered a series of neural stimulators to take control of Keevan's body and motor functions, thereby making it appear as if he was alive long enough to secure Ishka's release.
After killing the Jem'Hadar and capturing the Vorta Yelgrun, the Ferengi left Empok Nor, leaving Keevan's body continually walking into a bulkhead due to a jammed transceiver, much to Nog's amusement. (DS9: "The Magnificent Ferengi")
"No, you don't. But that's all right. It's not important that you understand, only that you carry out my instructions precisely."
"Obedience Brings Victory."
"Yes. Yes, it does. Go."
"You know, Captain, if I'd had just two more vials of White you never would have had a chance."
"Hi. I'm Rom. This is Nog, that's Brunt."
"Rom, he doesn't care."
"Truer words have never been spoken."
"I'll advise you all to send final messages to your loved ones and make sure your wills are in order."
"Because the moment we leave this station, you'll have signed your death warrants. Now, if you don't mind, I'm going to take a nap."
"I hate Ferengi..." [collapses, dies]
After Shea auditioned for a role as a Romulan but didn't get it, the producers remembered him when the role of Keevan came up. "He had a certain look in his eyes that we noticed [...] He could give you this very unsettled feeling just by looking at you," recalled Producer Steve Oster. "After we saw him, we all looked at each other and said, 'We need to bring him in as a Vorta!'". (Star Trek: Deep Space Nine Companion (p. 497)) Shea's eyes weren't the only aspect that led to him being cast as Keevan. "His voice was suitably disturbing and helped land him the role," noted Ronald D. Moore. (AOL chat, 1997)
Coincidentally, Christopher Shea was cast as Keevan on his birthday, much to his pleasant surprise. Speaking of the character, Shea remembered, "I read the script and just loved it. It was a dynamite role, and so well written. It reminded me of Shakespeare in many ways." (Star Trek: Deep Space Nine Companion (p. 497)) Shea played character in both "Rocks and Shoals" and "The Magnificent Ferengi".
The script for "Rocks and Shoals" specifies the pronunciation of Keevan's name as "KEY-van". Additionally, for the scene in which Keevan is introduced, it describes him as, "a badly wounded Vorta" who is lying on a "makeshift bed." The script goes on to refer to him as "the sweating, miserable Vorta." 
When writing the character of Keevan in "Rocks and Shoals", Ronald D. Moore didn't base him on anyone in particular but tried to make him "as despicable as possible while making his motivations completely believable." (AOL chat, 1997)
Authors Mark Jones and Lance Parkin described the final scene in which Keevan's body is left walking into a bulkhead in "The Magnificent Ferengi" as "really quite distateful." (Beyond the Final Frontier, p. 248)
Keevan appears as a selectable commanding officer in the non-canon video game Star Trek: Deep Space Nine - Dominion Wars, in which he is also described as being "highly experienced and devious" though not a skilled commander.
Keevan's card in the Star Trek Customizable Card Game describes him as a "Conniving liar".