Hitler's Religion or Atheism

Hitler was baptised Catholic. Over whole his life he attended the services. He resused to change the faith and always said he was Catholic.

Nevertheless, his faith was not that sincere. For example, he was aware that Catholic doctrine contradicts scientific facts (quote from Mein Kampf):

Here again the Catholic Church has a lesson to teach us. Though sometimes, and often quite unnecessarily, its dogmatic system is in conflict with the exact sciences and with scientific discoveries, it is not disposed to sacrifice a syllable of its teachings. It has rightly recognized that its powers of resistance would be weakened by introducing greater or less doctrinal adaptations to meet the temporary conclusions of science, which in reality are always vacillating. And thus it holds fast to its fixed and established dogmas which alone can give to the whole system the character of a faith. And that is the reason why it stands firmer today than ever before. We may prophesy that, as a fixed pole amid fleeting phenomena, it will continue to attract increasing numbers of people who will be blindly attached to it the more rapid the rhythm of changing phenomena around it.

He admired the Christian fanaticism:

The greatness of Christianity did not lie in attempted negotiations for compromise with any similar philosophical opinions in the ancient world, but in its inexorable fanaticism in preaching and fighting for its own doctrine.

He had some regrets about the Christian methods:

Each one of us today may regret the fact that the advent of Christianity was the first occasion on which spiritual terror was introduced into the much freer ancient world, but the fact cannot be denied that ever since then the world is pervaded and dominated by this kind of coercion and that violence is broken only by violence and terror by terror.

He believed that there was no fundamental difference between Catholic and Protestant faith:

The two Christian denominations look on with indifference at the profanation and destruction of a noble and unique creature who was given to the world as a gift of God's grace. For the future of the world, however, it does not matter which of the two triumphs over the other, the Catholic or the Protestant.

In conclusion we can say that he was a practicing Catholic who did believe in God but did not believe in every Christian dogma that contradicted the current science.

I see Adolf Hitler more in a materialistic than a religious tradition. He seemed to hold largely instrumental, secularist views on religions, and from this perspective occasionally had quasi-benign things to say also about Jewish religion. The following quote (from Brigitte Hamann's Hitler's Vienna: A Dictator's Apprenticeship) is from communication by Hitler to Otto Wagener in 1930:

Through Moses the Jewish people received a rule for life and living one's life that was elevated to a religion which was entirely tailored toward the essence of one's race, and simply and clearly, without dogmas and dubious rules of faith, soberly and absolutely realistically contains what serve the future and self-preservation of the children of Israel. Everything is geared towards the well-being of one's own people, nothing toward consideration of others ... we no doubt have to recognize with admiration this incredible strength of the Jews' preservation of their race.

Perhaps his own religion (if there was any) was an odd blend e.g. of Germanic (as in Nibelungen), Christian (as in his native culture), Hindu (as in Aryans and Vedic traditions), and Buddhist (perhaps as in earlier comment) fragments. Overall, I think this is a question without a clear single answer.

Hitler definitively believed in some form of deity, and also believed, that God send him to Earth to rule it and get rid of the Jews and other "lesser humans".

The folkish-minded man, in particular, has the sacred duty, each in his own denomination, of making people stop just talking superficially of God's will, and actually fulfill God's will, and not let God's word be desecrated. For God's will gave men their form, their essence and their abilities. Anyone who destroys His work is declaring war on the Lord's creation, the divine will. - Adolf Hitler, Mein Kampf Vol. 2 Chapter 10

He was raised catholic, and used Christianity and Catholic church to his advantage, however it isn't clear, if he had considered catholic or christian himself, or was just using this to take control over people. Hitler definitively wasn't atheist, but we aren't sure if he was a christian, or believed in other form of deity.

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If you want more objective analysis look here What were Hitler's religious views? and here Was Hitler a Catholic, an Atheist, or otherwise? From the end If it is possible to conclude on such a complex subject, it would appear that Hitler was not an atheist, nor was he a Catholic.