By the Nuremberg laws you were fully aryan if four of your grandparents were recorded as Catholics or Protestants by birth in church archives (as opposed to Jews. Getting an Arierpass was purely a matter of religion.)

Phrenological definitions were first appealed to in German courts after the annexation of Bohemia in 1938. Now they had to differenciate between Aryan and non-Aryan christians and, aside from relatives with German names, you could appeal to the form of your skull. According to the anthropologists who churned out the numbers, like Ilse Schwidetzky, Hitler was, of course, the very paragon being of an Aryan.

The applicants for SS membership had to have an Arierpass and were firther grouped by race according to the earlier definitions of Heinz F.K.Günther. To him having blue eyes and blond hair made you "Nordisch" as opposed to the "Fällisch", "Ostisch" or "Alpisch". But being "Nordic" has not been a membership requirement. Hitler had the member №1.

Source: Vokabular des Nationalsozialismus by Cornelia Schmitz-Berning; Die Geschichte der SS by Heinz Höhne.

It is important to note as well that not only were the Nuremburg laws in place, but that Aryan as a definition was a much broader scope of many people of Caucasian/West Asian heritage. (Note, Jewish/Arabic etc are often noted as Semites. These didn't become tinged with anthropological/racial connotations till much later on).

The blonde hair/blue eyes Aryan ideal we know today as fawned over by the Nazis is known as Nordicism. The three most well known sub-categories of the Aryan race are Alpine, Mediterranean and Nordic. These sub-categories defined different traits attributed to different people of caucasian descent and was a textbook way of examining heritage - for example, someone with olive skin and dark eyes would be Mediterranean, those of Alpine descent would be shorter, squatter, slightly fairer.. You get the idea. These people were considered more the backbone of European society - the settlers and the workers.

The fascination with the 'aryan' race as you know it - that is, Nordicism - comes from the belief that those of Nordic descent are natural born leaders, aggressors, and also the strongest of all these categories. Their physical attributes make them more capable of leadership.

Hitler later became more quiet about this ideal especially later on. Though he was obviously still fascinated by the idea of Nordicism, and quite evidently wanted what was considered the previously assimilated race to dominant again, a large portion of the fascination with Nordicism actually came from other Nazi party members, especially Hans Gunther who was awarded for his anthropological studies. Though Hitler was open about his fascination with the Nordic race, it was more of a collateral with many other ideals.

I heard he also considered certainnative american tribes aryan, is this true?

Quoting myself from previous instances of this question:

Blue eyes and blonde hair was an ideal, but German propaganda actually tended to downplay physical features when discussing the ideal Aryan. A Hitler Youth booklet called "Faith and Action" says: "Race means to be able to think in a certain way. He who has courage, loyalty and honor, the mark of the German, has the race that should rule in Germany, even if he does not have the physical characteristics of the “Nordic” race. The unity of the noble soul and a noble body is the goal to which we strive. But we despise those whose noble body carries an ignoble soul."

Hitler's actual definition of 'Aryan' sometimes changed based on what was politically convenient. Originally it was "white, non-Jewish" but it became necessary for him to add Slavs to those who were white but not Aryan. The lack of a specific definition allowed him to change it when it was convenient, as was the case in Yugoslavia with the Serbs being considered the "most Aryan" in the region... until a Serbian anti-Nazi coup forced him to declare the Croats the most Aryan.

From what I know Aryans aren't limited to blonde hair/blue eyes.... They also have dark hair/brown eyes and extend down to Iran and Northern India. Which is why Iran for example sided with the Nazis.

The idea of an Aryan race does not belong to Hitler, it was scientifically validated at the time by anthropologists and eugenicists. These racial ideas were not arbitrary, they were progressive and rooted in multidisciplinary scientific study (since discredited, eugenics is, of course, a pseudoscience). As such, it didn't matter whether Hitler himself conformed to these ideas, they were science, and therefore the best policy independent of Hitler himself.

I'm an anthropologist myself, and we like to hang our dirty laundry out to dry. The co-optation of the social sciences for this racial agenda was so total and powerful that anthropology at the time was known as "Rassenkunde", or literally, "racial studies". Robert Proctor writes a great article on this subject, "From Anthropologie to Rassenkunde in the German Anthropological Tradition" which I'll share with you if you PM me. From a summary I wrote of it for class:

Leading up to the rise of the Nazi regime, anthropologists were engaged in the study of race and genetics. This work was conducted “in a climate of growing conservative nationalism, and increasingly political anti-Semitism (Proctor 143)” and was willingly co-opted to further an agenda of eugenics. When the Nazis rose to power, academics would continue to “marshal an impressive array of scholarly works in support of Nazi racial science and policies (Proctor 172)” as anthropologists supporting the regime rose to positions of academic and social power. After the defeat of the Nazis, anthropologists writ large were quick to shift focus away from these ideas, “largely [as a] result of the shock and revulsion with which people reacted to the practical product of Nazi racial theory (Proctor 174).” Proctor ultimately concludes that “[t]here was nothing in the structure or methods of anthropological science in the 1920s or 1930s that inexorably led anthropologists to cooperate in programs of mass destruction (Proctor 175)”, but that the “normal science” nonetheless became a tool of evil for the Nazi party.