Neelix is a Talaxian originally from Rinax, a moon of the planet Talax, in the Delta quadrant, although his great-grandfather was Mylean. His entire family was killed in a conflict with the Haakonian Order. This forever haunts Neelix, although he masks it with his bright, constantly cheerful personality. He has a characteristically Talaxian physical appearance, with mottled temple ridges and a blond "hair tube" carefully arranged on the top of his head.
In the pilot episode "Caretaker", Neelix and his Ocampan partner Kes are rescued from the Kazon, and they join the crew of the USS Voyager. He arrives with his personal craft Baxial, which is utilized in later episodes. Neelix offers his services to Captain Kathryn Janeway, as a guide to the Delta Quadrant. He promptly appoints himself "Chief Morale Officer" and soon takes over the mess hall and becomes cook, as replicator usage has to be rationed in light of Voyager's limited power supplies. His cooking skills are very low at first, but improve with time (Harry comments on it in the "Mortal Coil" episode). Although Janeway simply tolerates Neelix at first, she later comes to respect and value Neelix as an important member of the crew eventually appointing him as unofficial ship's Ambassador after he proves his diplomatic abilities.
Neelix and Kes are romantically involved when they board Voyager, however, their relationship is later terminated by Kes under the control of an alien rebel during an away mission. Upon resolution of the conflict Kes decides to not re-initiate their intimacy (the alien's original rationale was based on Kes' own subconscious), though the two do remain good friends thereafter.
Neelix considers Security chief Tuvok a friend, and is always trying to "cheer up" the Vulcan. Tuvok, in turn, tolerates Neelix, his attitude hardly changes even after being fused with the Vulcan, creating a hybrid dubbed "Tuvix" during a transporter mishap. But, they eventually resolve their issues, and become friends. Neelix is also close to Samantha Wildman and her daughter Naomi. During an event when Tuvok was seriously injured and lost his ability to control his emotions, he spent every second with Neelix. He told Neelix he respects him and considers him a deep friend. He initially refused to undergo a procedure to regain his control telling Neelix he did not want to go back to just "tolerating" him instead of being his friend. When Neelix decided to leave the ship to stay with a group of his own people, Tuvok gave him a final show of respect and appreciation by doing a small jig with his foot after Neelix declared earlier in the episode he would get the Vulcan to dance before their journey was over.
Neelix's religious views are never fully discussed, but for most of the series he believes in a Talaxian version of the afterlife. In the episode Mortal Coil he loses this faith after being clinically dead for several hours, and having no vision of an afterlife, after being brought back to life with Borg technology employed by Seven of Nine. Neelix is so distraught by this that he considers suicide, but Chakotay convinces him that life is worth living regardless of an afterlife.
Neelix leaves the USS Voyager in the final season episode "Homestead", when he goes to live on an asteroid-based colony of exiled Talaxians. Janeway appoints Neelix as the "official" Ambassador for Starfleet in the Delta Quadrant, and he bids the crew a fond farewell. He has a cameo in the series finale, "Endgame", establishing that, at least while Voyager remained in the Delta quadrant, Neelix does indeed stay in contact with his friends.