In 2356, the metreon cascade was used against the Talaxians on the Talaxian moon Rinax in an attempt to end a decade-long conflict. The Talaxian government gave their unconditional surrender the following day, thus ending the war.
Many Talaxians (and even some Haakonians) developed a deep hatred of Jetrel for having led the team that developed a weapon that caused so many deaths. Jetrel tried to justify himself, saying that he was not a "monster" because he did not use the cascade, he merely invented it. While he called the weapon an inevitable scientific discovery, Jetrel was nonetheless involved. He considered the use of the weapon necessary at the time, had no apparent regrets in developing it, and only realized the seriousness of what he had done when his wife Ka'Ree left him for his apparent lack of remorse, taking their three children with her – in his words, "my own casualties of war." Jetrel also later learned that there had been unanticipated aftereffects of the cascade among its survivors, including the terminal blood disease metremia.
Jetrel spent the remaining years of his life attempting to undo some of the damage his weapon had caused by trying to find a cure for metremia, and also began his work on regenerative fusion. When Jetrel presented his theories on regenerative fusion to the Haakonian Order, he was deemed a Talaxian sympathizer and exiled from his homeworld.
In 2371, Jetrel encountered the USS Voyager; knowing that Neelix, a Talaxian, was on board the ship, Jetrel ostensibly wanted to screen Neelix for metremia, as Neelix was in one of the scout parties looking for survivors on Rinax. Neelix was extremely uncooperative with Jetrel, blinded by anger at the scientist whose weapon had wiped out his entire family and hundreds of thousands of others on Rinax. With persuasion from Kes, he finally agreed to be screened. Unfortunately, he was diagnosed with incipient metremia.
Jetrel was fascinated with Voyager's transporters and studied them in depth. In time, his true purpose was revealed: he believed that the transporters could be used to restore the bodies of those vaporized by the metreon cascade more than fifteen years earlier, effectively bringing them back from the dead. He passed his findings on to Captain Janeway and persuaded her to travel to Rinax to attempt his experiment in regenerative fusion. Voyager made its way to Rinax, and Jetrel persuaded Janeway to allow him to use the transporters to try to restore those who were killed by the metreon cascade, but his experiment failed. Jetrel then revealed that Neelix did not have metremia; ironically, it was Jetrel who had the disease, in its final stages. Before his death, Neelix forgave Jetrel. (VOY: "Jetrel")
Jetrel was played by veteran Star Trek actor James Sloyan. Kenneth Biller thought he "did a great job." (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 146) The costume worn by Sloyan as Jetrel was sold off on the It's A Wrap! sale and auction on eBay. '
In general, the character of Jetrel was based on American scientist J. Robert Oppenheimer, who helped invent the atomic bomb but was fraught with misgivings over its later use. "So is it unsympathetic? I don't know," Michael Piller contemplated, regarding the portrayal. "I look at that show and I find the Jetrel character tortured. And I think Oppenheimer was. He's trying to correct a grievous wrong. I think that the character is not an unsympathetic one." (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 147)
The parallels between Jetrel and Oppenheimer remain obvious in the episode (as do similarities between the metreon cascade and the use of atomic weapons by the United States against Japan, ending World War II). On the other hand, Neelix actor Ethan Phillips likened Jetrel to "Eichmann or Hitler or Genghis Khan." ("Voyager Time Capsule: Neelix", VOY Season 3 DVD special features)