I was curious as to whether the Hydra of the MCU or the Da'at Yichud of Wolfenstein had actually been based on concepts within the Nazi party and after reading on Reddit and other sourcesI found out that Himmler actually belived in this, and I'm quite confused as to why he belived in this, he would have to have been intellegent to get to his position of power, so does anyone know why he beived in the occult?
So, you are correct that Himmler was quite the occult guy. He took inspirations from all sides and was both favorable to old Germanic cults and, interestingly, to islam, which was also liked by Hitler for its militaristic stances. However, it is also to be assumed that these influences on nazi culture were overdrawn by writers like of the Wolfenstein games for measurements of entertainment.
Let's get straight to your question then: Why was Himmler occult? Well, that's, as with many religious questions, hard to answer.
According to Goodrick-Clarke, who wrote a book on the nazis and occultism in the eighties, Himmler early on was connected with Ariosophism, a religious movement in Germany, especially the south, and Austria.
The name had been established during World War 1 and the cult was somewhat popular until World War 2 with a select number of people. Ariosophists believed in the supremacy of the Aryan race and connected it with a few occult traditions, partially of pre-christian religious movements, including astrology and palmistry. The movement believed that, while most people were descendant from human tribes in East Africa, a select few, the Aryan master race, had lived in Scandinavia for millenia, a master race destined to rule the world. They even formed the New Templar Order ("Neutemplerorden", with the fancy latin name Ordo Novi Templi) to connect their beliefs with christian traditions. The movement, before being known as Ariosophism, also called itself Ario Christianity and Theo Zoologia. Goodrick-Clarke however does not believe that these people around Jörg Lanz von Liebensfels gave Hitler his ideas, something that was theorized by historians in the fifties and sixties.
Back to Himmler. He was, on a nonreligious level, a racist through and through, but also deeply involved with the occult from his childhood or at least his late teenager years. He basically tried to find old cults and teachings proving Aryan supremacy. Christianity with its emphasis on loving one another would not do.
He gave the SS, which he controlled, a certain amount of mysticism and symbolism. He chose a skull as an important symbol, something pretty bold for an organization which in name was defensive ("Schutz"staffel). Also, the double S that became the organization's main symbols were Germanic runes that were created by an Austrian occultist by the name of Guido von List, in 1906. While runes similar to the runes by Von List had actually been used, most Germanic peoples did not develop advanced scripts or literature.
But I am driving around your question. Why was Himmler occult exactly? I can not give you a more precise reason than his strict religious and spiritual upbringing, his racist tendencies, his obsession with the Order of the Teutonic Knights and their crusades against slavic peoples and his early contacts with occult movements like the Ariosophists. His diaries and letters that recently surfaced, as far as I can tell, go back to 1927, skipping 27 years of his life. By '27, he was already anti-semitic, racist and obsessed with Aryan supremacy on a proto-christian basis.
The primary source used for this extract was The Occult Roots of Nazism by Nicolas Goodrick-Clarke, year 1985. It is a highly interesting read if you want to pursue the topic further.
Other sources:
Hein, Bastian: Elite für Volk und Führer? Die Allgemeine SS und ihre Mitglieder 1925–1945 (language: German)
Mazower, Mark: Hitlers Imperium. Europa unter der Herrschaft des Nationalsozialismus (language: German)
Wucher, Mark: Marksteine der Deutschen Zeitgeschichte (language: German)