Implicitly I always thought that the ideology of antisemitism and the drive to genocide of the Jews came from Hitler.
I know very well that Hitler was in a way fitting into a general environment of disliking/hating Jews at the time. But how much of the twisted ideology of the Nazis was Hitler personally and how much was the party itself (or other key people)?
What if another person became the leader, would they have still driven Germany to do the holocaust or was it really a sort of personal vendetta of Hitler.
In way I also want to know whether he was the real person in power or also a figurehead in some way.
In a weird way, he was almost both. I say "almost" because Hitler wasn't a figurehead--he was absolutely the guy with the most authority--but he wasn't an especially hands on leader.
There are two main schools of thought on Hitler's weak leadership style. First, a process Ian Kershaw called, "working towards the Führer." Kershaw is examining various forms of authoritarian regimes, but he contends that in the case of Nazi Germany, Hitler's rule is largely hands-off and irrational. Not in the sense that killing all the Jews in Europe is irrational, but rather a more abstract sense along the lines of, "does what we're doing today logically follow from what we did yesterday?" Since winning Hitler's approval was the measure of success, and since Hitler himself rarely issued detailed policy measures, his subordinates would compete amongst themselves for his attention, resorting to ever-more radical means to do so. Hitler would issue a vague order like "solve this problem" without suggesting how it might be solved. Left to their own devices, subordinates would often (but not always) devise extreme solutions.
Hans Mommsen describes Hitler as a "weak dictator." There's some overlap between Mommsen and Kershaw here, but they're coming from very different places historiographically. Mommsen is probably the guy when it comes to structuralism and he's not at all interested in conceding that ground. (Kershaw is neither an ardent intentionalist nor an ardent structuralist.) Mommsen contends that rather than driving the ever-radicalizing Nazi party, Hitler himself was radicalized by it, famously writing, "Hitler was just one extreme element of the extensive malevolence that was the Nazi system." Hitler made decisions when pressured from below instead of creating new ideas/policies himself.
Finally, I'll briefly plug Kershaw's classic The Hitler Myth. Hitler wasn't a figurehead, but the public projection of his persona was deeply mythologized by Goebbels and others. So in this sense, there was a fissure between the popular perception of Hitler as a singular master of politics and the reality of the degree to which Hitler involved himself in the day-to-day running of the Third Reich.