Professor Gideon Seyetik (portrayed by Richard Kiley) was a guest character who appeared in the Star Trek: DS9 episode "Second Sight". He was regarded as one of the greatest minds in the Federation, reknowned for his accomplishments in terraforming. No one was more proud of Seyetik's achievements than himself, of course, and he would frequently remind others of the fact. He had a tendency to ramble on about his work and freely admitted he was a slave to his own towering ego. He also had a reputation for remarriage, his latest marriage being to a Halanan named Nidell.
In 2370, Seyetik undertook his last great project: reigniting the dead star Epsilon 119. He invited Commander Benjamin Sisko and the senior staff of Deep Space 9 aboard the USS Prometheus to witness the event, and during their time on the ship, Sisko met Nidell, who looked exactly like a mysterious woman that had recently visited him on DS9 that he had become infatuated with. Sisko spoke to Nidell, believing she was in fact Fenna, but Nidell insisted that she and Sisko had never met before.
When Fenna reappeared on the Prometheus, Seyetik revealed the truth: Fenna was a psychic projection created by Nidell. Nidell's race were all capable of this telepathic ability, but it could go out of control during times of great emotional stress and could be damaging, even fatal. Nidell had lost consciousness when Fenna manifested and Seyetik believed that her ailment was due to her being unhappy in her marriage to him. Because Halanans mate for life, Nidell could not leave Seyetik.
Later, Seyetik put his project to reignite Epsilon 119 into action, but instead of operating his shuttlepod remotely as he had originally planned, he boarded the shuttle and piloted it manually, flying toward the dead star carrying a protomatter device that would reignite it. He knew that flying in himself would kill him, but he decided that he loved Nidell too much for her to die whilst anchored to him and decided that killing himself would set her free from the bonds of her marriage. Seyetik maintained communications with the Prometheus up until the moment his shuttlepod crashed into the star's surface. As hoped, the protomatter aboard the pod reignited the star, and so Seyetik's sacrifice saw the final fruition of his life's work as well as the release of his wife.