Laas was a Changeling and one of the Hundred Changelings that were sent by the Founders to gather information on the solids they encountered. Like the Founders, Laas had an established distrust of solids based on experience. However, he would set out to find the other Hundred and create a new Great Link.
Life on Varala
Laas ended up on the planet Varala, home of the Varalans, in the 22nd century. They named him "Laas" which, in the Varalan language, means "changeable" – a name Laas considered to be very unimaginative, but he kept it. Laas was initially fascinated with humanoid life, and, not long after Laas learned to assume humanoid form, he found a Varalan mate. The relationship did not last, however, because the couple could not have children, something that was very important to the Varalan woman. Laas would spend decades as a humanoid, but eventually came to find it limiting, even coming to the conclusion that humanoids were destructive to their environments. For example, Laas once assumed the form of a volg and migrated to the southern continent with a herd. When Laas returned with the herd the next summer, the herd's breeding grounds had been fenced off. Events like this would shape his opinion, and he preferred primitive lifeforms which did not deceive or lie.
In 2375, Laas eventually sensed the presence of Odo on a Danube-class runabout – it was the first time Laas had met another changeling. He allowed himself to be under his custody, trusting Odo immediately. Upon returning to Deep Space 9, Laas was placed under Odo's supervision. Odo taught Laas of life in the Great Link by linking with him, as well as the nature of the rest of their species. Laas was elated by the experience of linking with Odo, helping him understand how he was meant to exist. Odo and Laas speculated that either Odo was sent out after he had been, or Odo had been adrift for a long time before he was discovered.
Despite minor differences in physical appearance, Laas considered all humanoids basically the same, compared to himself. He believed humanoids were intolerant of differences. Odo also tried to show Laas that not all 'solids' were as intolerant as the ones he had met, but Laas was unconvinced, believing Odo was still in a stage where he was fascinated by their existence and also was conditioned by his peers to become humanoid in a sense. He believed this led Odo to believe he was accepted, when it was really a farce. Laas instead wanted Odo to come with him to search out the other Hundred, but Odo resisted.
Laas often spoke his mind, and had no problem with being himself and changing form in the presence of others. He insulted Odo's friends when he met them, and told Odo his relationship with Colonel Kira Nerys would not last. Later on Deep Space 9's Promenade, Laas turned himself into fog to relax, something that unsettled many people there. When he changed back to humanoid form, two Klingons immediately confronted him. The Klingons became angry and attacked Laas, and Laas killed one of the Klingons. Laas was placed in a holding cell, and General Martok asked that Laas be turned over to the Klingons. Kira, having suspected Odo was in conflict between her and Laas, helped Laas to escape, believing that Odo wanted to join him in his search. Laas did not understand why, but he left.
Laas waited at an abandoned mine on Koralis III, and was pleased to see Odo came as well. However, Odo wished Laas good luck on his search and returned to DS9. Laas promised to create a new Link and send for him. (DS9: "Chimera")
Laas was played by J.G. Hertzler, credited as Garman Hertzler at his own request. Hertzler felt that this was necessary to separate the role from his recurring character of Martok. Other actors considered for the role included Jeffrey Combs and Andrew Robinson, but it was felt that those actors would be too recognizable. (Star Trek: Deep Space Nine Companion (pp. 656-657))
Hertzler partially based Laas' distinctive way of speaking on William Shatner: "I wanted to find a way to keep this character sort of annoyingly judgmental, because of his politics. He felt that these humanoids were so far beneath him that it was like talking to dogs. His pro-environmentalist point of view, feeling that humanoids ruin things, seemed like almost a passionate adherence to the Prime Directive. And that reminded me of James Kirk. William Shatner has a theatrical way of delivering lines by taking breathing pauses and holding onto the ends of words. I thought, 'That would work for Laas.' So that's where the voice came from. It's me doing my best imitation of Laas doing William Shatner doing Kirk!" (Star Trek: Deep Space Nine Companion (p. 657))
Hertzler came up with his own backstory for the name. He remarked, "Laas has these wonderful speeches that question the very foundation of the Federation, where people of all religious and racial backgrounds come together to live in peace and harmony. Basically he's saying, 'Forget about it. It's not possible. It violates the laws of nature.' To me, his name was laws." (Star Trek: Deep Space Nine Companion (p. 658)) According to the script, the pronunciation for Laas was "LAH-z".
Episode writer René Echevarria has been unable to recall exactly why he called the character Laas, but he did note that "I wanted his name to be something really strange and unusual. Ira kept making fun of it. Whenever we would talk about the story, Ira would say, 'And then the Swedish guy comes in...'" (Star Trek: Deep Space Nine Companion (p. 658))
Presumably, when he linked with Odo, Laas became infected with the morphogenic virus Odo was unknowingly carrying at the time. The producers realized this, but did not have time to address it in an episode before the series ended. Ira Steven Behr expressed his regret at not being able to bring Laas back. He notes that "that has nothing to do with whether he was sick or not. I just liked the character." (Star Trek: Deep Space Nine Companion (p. 658))
The script describes Laas' alternate form as a "spacefaring lifeform", its "body is smooth and cylindrical, and it propels itself with a pulsating motion. As it "swims" alongside the Runabout, we see that it's almost as big as the ship." (Star Trek: Deep Space Nine Companion - A Series Guide and Script Library, )
Originally, in order to save on budget, consideration was given to simply reusing footage of the space-dwelling lifeform from the Star Trek: Voyager episode "Elogium", before being created as a newly designed CGI. (Star Trek: Deep Space Nine Companion (p. 658))
The script's spacefaring lifeform was designed by Senior Illustrator John Eaves, who described it in his sketch as "space swimmin' changelin' thing". In his concept art he explained how the form travelled through space, where the aft tendrils were explained as: "Entity is positively charged and magnifies the opposite polarities, thus repeling [sic] its form in a zero g, zero atmospheric conditions, motion is acquired by this feature." The forward spikes were labeled to indicate that "negatively charged space particles enter here." (Star Trek: Deep Space Nine Companion (p. 657))
In the Deep Space Nine relaunch, Laas returned to the Great Link. He was often sent to speak to Odo when he took solid form, such as in Avatar, Book Two and Worlds of Star Trek: Deep Space Nine Volume 3. After the Great Link dissolves following the discovery that the only means of Changeling reproduction has been killed, Odo and Laas were left as the last of the Dominion. Seven years later, Odo and Laas have managed to rediscover around forty changelings, but are separated when the apparent destruction of the Bajoran wormhole leaves Odo trapped in the Alpha Quadrant in Plagues of Night and Raise the Dawn.
Loading-screen tips shown on Star Trek Online mention that the Founders broke all ties to Laas, declaring all Alpha Quadrant Changelings "renegades"; Changelings (and Jem'Hadar) appear in the game as hostile NPCs. In the mission "The new Link", the player fights and captures Laas under the direction of another Changeling.