Seamus (pronounced "SHAY-mus") was a character in Tom Paris's holoprogram called Fair Haven. He frequently had troubles with his wife and often asked members of the USS Voyager crew for a bit of money for a drink at Michael Sullivan's pub.
After seeing Tom Paris crash his automobile, he saw Paris' tire magically repair itself. He immediately headed to Sullivan's Pub, and told its inhabitants that he believed Paris was from the spirit world. Seamus followed Paris and Harry Kim, and saw Maggie O'Halloran turned into a cow as Kim kissed her, which Paris did as a joke. Seamus cited it as further proof that the visiting Voyager crewmembers were wicked spirit folk and that they had come to destroy the village.
He led a group of armed villagers who took the crew captive. Seamus attempted to banish them to the other world by reading incantations from an ancient book. When this did not work, he was in favor of burning them as witches. He and the town people were persuaded to let them go by Michael Sullivan. (VOY: "Fair Haven", "Spirit Folk")