Fyodor Mikhailovich Dostoyevsky, author of such works as Crime and Punishment and The Brothers Karamazov, was a devout Orthodox Catholic from a very young age. He is reported to have, at a young age, recited prayers to guests to their great amazement. He is also said to have been greatly affected by various Bible selections. Through his time in the military academy, he continued the devout lifestyle that he had developed as a child, reading religious texts on a regular basis. However, over time he developed beliefs closer to those of the old believers than the mainstream Russian Orthodox Church. However he later wrote various contradictory things such as:
[I was a] child of unbelief and doubt up to this moment, and I am certain that I shall remain so to the grave.
[E]ven if someone were to prove to me that the truth lay outside Christ, I should choose to remain with Christ rather than with the truth.
However, later during his Siberian exile he again publicly revered Christ. However, he avoided churches and institutionalized religion. At no time though, did he become stuck in his ways. At times, he explored other religions, including Islam through reading the Quran. He described himself only as a "philosophical deist". However, his writings in The Brothers Karamazov where he states belief in the holy trinity brings into question his understanding of the terminology he used.
Unfourtunately much of this is sourced from a few Wikipedia articles because the sources they used are not available to me in this location because they are all print books, which are not to be found in libraries near me.