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Religious affiliation

Although Fischer's mother was Jewish, Fischer rejected attempts to label him as Jewish. In a 1962 interview with Harper's, asked if he was Jewish, he replied that he was "part-Jewish" through his mother. In the same interview he was quoted as saying: "I read a book lately by Nietzsche and he says religion is just to dull the senses of the people. I agree." In a 1984 letter to the editor of the Encyclopaedia Judaica, Fischer demanded that they remove his name from future editions.

Fischer associated with the Worldwide Church of God in the mid-1960s. The church prescribed Saturday Sabbath, and forbade work (and competitive chess) on Sabbath. According to his friend and colleague Larry Evans, in 1968 Fischer felt philosophically that "the world was coming to an end" and he might as well make some money by publishing My 60 Memorable Games; Fischer thought that the Rapture was coming soon.

During the mid-1970s, Fischer contributed significant money to the Worldwide Church of God. In 1972, one journalist stated that "Fischer is almost as serious about religion as he is about chess", and the champion credited his faith with greatly improving his chess. Yet prophecies by Herbert W. Armstrong went unfulfilled. Fischer eventually left the church in 1977, "accusing it of being 'Satanic', and vigorously attacking its methods and leadership".

Towards the end of his life, Fischer became interested in Catholicism. He bought his friend Garðar Sverrisson a copy of "Basic Catechism: Creed, Sacraments, Morality, Prayer" so Sverrisson could explain the religion better to him. According to Sverrisson, Fischer talked to him about transformation of society through creation of harmony and that "the only hope for the world is through Catholicism." Fischer was also known to have read a synopsis of G. K. Chesterton 's works in the years leading up to his death. He requested a Catholic funeral, and this final service was presided over by Catholic priest Jakob Rolland.