There is no question that Hitler was a Nazi. Nazism was clearly his most important religious affiliation, not in the positive way the word "religion" is often defined, but in the general sense that any philosophy or belief system which is most important in a person's life is that person's "religion," regardless of whether or not it is universally labelled as a "religion." Hitler was also born into a Catholic family, but he rejected Catholicism and in most ways he rejected Christianity in general. On occasion we have read people claim that "Hitler was a Catholic" or "Hitler was a Christian" in a meaningful way, implying that Christianity or Catholicism was the primary impetus for his Nazi reign. Such claims are simply vitriolic attacks occasionally voiced by ideologically-inclined anti-Christian, anti-Semitic or pro-Nazi people. Historians agree that Hitler was pointedly anti-Christian. We are not aware of any published sources from acknowledged academic historians or writers that identify Adolf Hitler as significantly Catholic or Christian in his motivations as an adult. If anybody writes to us to point out such resources, we will be happy to cite them and refer to them here. One detailed publication that describes how Hitler was anti-Christian was written by Jewish writer Julie Seltzer Mandel, as described by Matt Kaufman (http://boundless.org/2001/regulars/kaufman/a0000541.html):
I vividly remember a high school conversation with a friend I'd known since we were eight. I'd pointed out that Hitler was essentially a pagan, not a Christian, but my friend absolutely refused to believe it. No matter how much evidence I presented, he kept insisting that Nazi Germany was an extension of Christianity, acting out its age-old vendetta against the Jews. Not that he spoke from any personal study of the subject; he just knew. He'd heard it so many times it'd become an article of faith - one of those things "everyone knows."... Well, sometimes myths die hard. But this one took a hit in early January, at the hands of one Julie Seltzer Mandel, a Jewish law student at Rutgers whose grandmother survived internment at Auschwitz.From: Jadwiga Biskupska (Cornell University), "Hitler & Triumph of the Will: A Nazi Religion in the Catholic Style" in Undergraduate Quarterly, September/November 2004, page 147 (URL: http://www.undergradquarterly.com/EJournal/2004Q2/Biskupska.pdf):
A couple of years ago Mandel read through 148 bound volumes of papers gathered by the American OSS (the World War II-era predecessor of the CIA) to build the case against Nazi leaders on trial at Nuremberg. Now she and some fellow students are publishing what they found in the journal Law and Religion (www.lawandreligion.com)... The upshot: a ton of evidence that Hitler sought to wipe out Christianity just as surely as he sought to wipe out the Jews.
The first installment (the papers are being published in stages) includes a 108-page OSS outline, "The Persecution of the Christian Churches." ...how the Nazis - faced with a country where the overwhelming majority considered themselves Christians - built their power while plotting to undermine and eradicate the churches, and the people's faith... From the start of the Nazi movement, "the destruction of Christianity was explicitly recognized as a purpose of the National Socialist movement," said Baldur von Scvhirach, leader of the group that would come to be known as Hitler youth. But "explicitly" only within party ranks: as the OSS stated, "considerations of expedience made it impossible" for the movement to make this public until it consolidated power... By 1937, Pope Pius XI denounced the Nazis for waging "a war of extermination" against the church... Catholic priests found police snatching sermons out of their hands, often in mid-reading
...the notion that the church either gave birth to Hitler or walked hand-in-hand with him as a partner is, simply, slander. Hitler himself knew better. "One is either a Christian or a German," he said. "You can't be both."
Catholicism and Nazism have a more complicated relationship than some might think. Hitler both despised and admired various aspects of the Roman Catholic Church. Though the Nazi movement was superficially areligious, even anti-religious, the Nazi's greatest piece of propaganda and self-aggrandizement, Leni Riefenstahl's 1934 film about the Nuremberg Party Rally, Triumph of the Will, is in many ways profoundly religious. The film both makes use of Catholic religious imagery and draws on the Catholic sacramental tradition to give dignity and legitimacy to its construction of Adolf Hitler as the "god" of the Nazi movement... Since the beginning, Catholicism and Nazism had an uncomfortable coexistence. They jarred long before Riefenstahl began filming Hitler's rally in the summer of 1934... The Concordat, along with many other more famous agreements and treaties signed by the Fuehrer, was quickly violated, and the Church was ineffective in protecting Catholics from all manner of religious and cultural harassment. Alfred Rosenberg, the closest Nazism as an ideology ever came to having a philosopher, was consistently and virulently anti-Catholic... Hitler himself was not purely or simply anti-Catholic or anti-Church, and certainly not so before his rise to power. He was a baptized Catholic, as was his propaganda minister, Joseph Goebbels, and a number of other prominent members of his administration. Interestingly, though both men rejected their Catholic faith and recognized that they had excommunicated themselves, neither ever formally left the Church and dutifully continued to pay church taxes until their respective deaths. Hitler's own mother, to whom he was very close, was a devoted Catholic, and Hitler received Catholic schooling during his childhood in Austria... In his extensive, often contradictory writings and "table-talk," Hitler reveals an ambivalent attitude toward the Catholic Church. As an institution on German soil, he is very much opposed to it, and he ridicules the teachings of Church fathers and the practice of the Catholic faith... he detested the doctrines, of the Roman Church... Institutionalized religion, in Hitler's view, was a waning phenomenon...
There is also some dispute about the extent to which Hitler was influenced by paganism or German Neo-Paganism. Many sources are available that identify Germanic pagan influences on Hitler. But I have seen no credible evidence that Hitler was an adherent of Neo-Paganism in the contemporary post-1960 sense of the word, nor have I read anything to indicate that Hitler ever explicitly identified himself as a "Neo-Pagan."
"Adolf Hitler's religious beliefs" on Wikipedia.org