Ohlmarks translated the Sagan om Ringen, Sagan om de två tornen and the Sagan om konungens återkomst. They were considered very bad by Tolkien, who expresses a strong dislike in Letters 228 and 229. He wrote Guide to the Names in The Lord of the Rings to prevent further wrongdoing in translations. See also the link, "Lord of the Errors", below.
Two years before his death, he blamed Swedish Tolkien fans for a fire to his house, and wrote Tolkien och den svarta magin, "Tolkien and the Black Magic". In it, he concocted a conspiracy theory that claimed Tolkien, and the Tolkien Society, practised black magic and Nazi occultism.