Suder was a Betazoid, but unlike most of his species, he seemed to be neither empathic nor telepathic. This may have been caused as a side effect of whatever mental illnesses he was suffering from. Earlier in his life, he had tried a number of treatment options for his condition including violent holographic programs and targeted synaptic therapy. Neither of these were successful.
He joined the Maquis in 2370, though his homeworld was not under threat. He worked under Chakotay and was an effective member of the Maquis although he did not engender much affection from his colleagues. They regarded him as too efficient when killing Cardassians and this made them uncomfortable around him. In fact, Suder was using the Maquis as a release valve for his uncontrollably violent nature.
A brief investigation by Tuvok uncovered his crime. Because of the lack of punishment or rehabilitative options, he was put under house arrest in his quarters. A Vulcan mind meld by Tuvok was carried out with the aim of helping Suder to control his impulses. While this proved to be somewhat effective, the resulting trauma to the Vulcan's emotional systems resulted in him losing some of his own control, becoming dangerous and violent.
Over the next few months, Suder worked with Tuvok to learn how to maintain his self-control. Additionally, he began to find enjoyment in other activities. Under Tuvok's guidance, he began to learn about Orchid breeding and eventually became proficient at genetic manipulation of plants. He wanted to use these talents to contribute to the ship in a positive way by increasing the output of the ship's airponics bay. Captain Janeway, however, was unsure about allowing him more privileges. (VOY: "Basics, Part I")
This progress came to a halt when Kazon-Nistrim agent Jal Tierna detonated a biological explosive on Voyager. The explosion took place adjacent to Suder's quarters and the Betazoid was believed killed. While the ship was taken over by the Kazon, Suder hid in an access conduit and managed to make it to sickbay where he found The Doctor, who was already planning to retake the ship when Suder arrived. During their sabotage efforts, Suder was forced to kill a Kazon soldier. Despite The Doctor's assurances that he had done the right thing, he succumbed to a panic attack as he had been working so hard to avoid his violent impulses.
Suder was instrumental in helping the crew retake Voyager from Seska and the Kazon. After The Doctor was deactivated by Seska, Suder was left alone to disable the backup phaser couplings, but was slightly comforted by a message The Doctor had left him, in which he assured Suder that he had The Doctor's complete confidence; Suder had already shown great loyalty and dedication to his crew. With this in mind, Suder was able to sneak into engineering and launch a surprise attack, killing eleven Kazon soldiers single-handedly. After killing the Kazon that were holding engineering, he was able to sabotage the backup phaser coil, causing it to explode when it was activated (Tom Paris having disabled the primary couplings). He was killed by a Kazon soldier in the process. Thanks to Suder's bravery, Voyager was able to be retaken, making it possible for the entire crew to continue on their journey back home to the Alpha Quadrant. After the crew were back on Voyager, Tuvok spoke briefly over Suder's body after The Doctor and Paris had told him of Suder's heroism, offering him a Vulcan prayer wishing that, in death, Suder would find the peace that he could never achieve in life. (VOY: "Basics, Part II")
He would later be named on a list of telepathic casualties Devore Commander Kashyk confronted Captain Janeway about in 2375. He was the only member of the list actually dead, the rest hiding in transporter suspension. Janeway explained to Kashyk that Suder died in a "conflict with a species called the Kazon." (VOY: "Counterpoint")