"Fine, I'll kill you later."
In 2285, Maltz participated in Kruge's attempts to obtain and exploit the Federation's Genesis technology. Kruge showed him the stolen summary of the device, and he was impressed and sworn to secrecy. While in orbit at Genesis, Maltz manned the sensors and identified the USS Enterprise on approach. Despite Kruge's apparent success of capturing the vessel via a boarding party led by Torg, Maltz witnessed its destruction that killed much of the crew. He then commanded the ship when Kruge went to the planet to kill James T. Kirk. Kruge ordered him to beam up all but Kirk; however, unaware Kruge had been killed afterwards, he was tricked into beaming him up as well. As he was the only crew member left aboard, they commandeered the ship. When Kirk presented an ultimatum to Maltz to either assist them or be killed, Maltz simply responded, "I do not deserve to live," to which Kirk replied, "Fine, I'll kill you later." After successfully escaping the destruction of the Genesis planet, Kirk ordered Pavel Chekov to have Maltz imprisoned, an act which surprised the Klingon, as he was expecting Kirk to kill him. When Maltz confronted Kirk with his earlier promise, Kirk simply said, "I lied." He's subsequently briefly seen taken into custody by Vulcan security shortly after the ship lands on Vulcan. (Star Trek III: The Search for Spock)
Preparing and performing the role
Maltz was played by actor John Larroquette. He was highly eager to feature on Star Trek in any capacity. Recalling how he wound up with the part, he stated, "I was just called and asked. And I ran [....] Leonard Nimoy and I got together, and I read some of the script with him. I guess the idea of playing a Klingon was real fascinating to me [....] Nimoy knows that form inside and out, obviously, and since I had never played a Klingon before, it was sort of like, 'No, this is how Klingons talk.'"
When asked if he did any other preparatory research for the role – such as watching past Star Trek episodes or consulting other actors who had played Klingons – Larroquette answered, "Yeah. I talked to a couple of old Klingons at the Old Klingon Home." He found his part as Maltz was difficult to speak about seriously, in general, remarking, "How can you talk seriously about a role where you spent the whole day with a crab on top of your head?"
While portraying Maltz, Larroquette did not find his strengths as a performer were stretched, considering the long hours of makeup application required for the role. Despite this as well as the fact that he was barely recognizable – even to his fans – under the amounts of makeup and body-armor costuming involved in the part, he thought that playing the Klingon "was fun, a lot of fun."
In a 1989 interview, John Larroquette declared that he "absolutely" would be interested in reprising the role of Maltz. He deadpanned, "I just kept telling [...] [Kirk actor] Bill Shatner–since I was the last surviving Klingon, I smell spin-off. I could take this to a series. Maltz starts off and he has a little hot dog stand on Yakka III out there in the Doofus Galaxy." (Starlog, issue #138, p. 25)
It is unclear what became of Maltz after Kirk took the Bird-of-Prey to Vulcan. He may have become a Federation prisoner of war, though the Klingon Ambassador made no mention of him when demanding Kirk's extradition in Star Trek IV: The Voyage Home. According to John Larroquette, the fact that Maltz "winds up in prison at the film's end" sparked a campaign conducted by a New Zealand fan network who called themselves the Klingon Occupation Force. Apparently half-joking, Larroquette commented, "It's very interesting [....] They have this huge 'Free Maltz' campaign. They want to get him out of prison. I get mail from them all the time." (Starlog, issue #138, p. 24)
In The Klingon Dictionary (2nd ed., p. 12), Maltz is credited for revealing the Klingon language to the Federation and to Marc Okrand. In Star Trek: Enterprise, Vulcans had the language stored in their database from previous contacts and Hoshi Sato was able to translate the language. According to Okrand, Maltz's name is matlh in tlhIngan Hol. (The Klingon Dictionary 2nd ed., p. 58)
In the novelization of Star Trek IV: The Voyage Home, the Federation claimed that Maltz committed suicide; the Klingon Ambassador suggested that he was murdered to hide the truth about the Genesis Device.
In the Klingon Academy game, which is told from the Klingon Empire's point of view, official information is conspicuously adamant on insisting that all rumors about Maltz surviving the events of Star Trek III are false and that he did not assist the Federation in translating the Klingon language. Nor would a true Klingon allow himself to be taken prisoner by the Federation.
Alternatively, in the Genesis Wave book series, it is revealed that Maltz survived, but was disgraced by his loss of honor, causing him to hide away from Klingon society for several years before the coming of the Genesis Wave. With the Wave, Maltz's life gained a new purpose, and he tracked the wave to its source on a Klingon vessel under the command of Leah Brahms, who had won his respect due to her determination to warn others about the Wave and avenge the death of her husband. Eventually, after becoming separated from the others, Maltz acquired a Defiant-class starship which he used to get on board the asteroid base that was preparing to launch a second Genesis Wave. There, accompanied by Carol Marcus, he set the station to self-destruct, regaining his lost honor as they prevented the Wave from ever being used again.