The Superman is the intermediary between Man as he is now and the Supramental being. The Superman is someone who is born in the usual normal human animal way but his inner consciousness is transformed enough to belong to the higher kind. It is the Superman who will subsequently lead the way to the fully transformed (inner and outer, including physical transformation) Supramental being.
This being did not wait for Hitler’s death, it is there that you are mistaken. These beings are not at all tied to a single physical presence.