in the chosen who is father of hasidism

It's difficult to pinpoint exactly what you're asking here. Is it something like: whose father is a Hasidic Jew? If this is your question, then the answer is Danny's father, Reb Saunders. In fact, his Hasidism forms the main context in which Danny's struggle must mature.

I think the answer you are looking for can be found in Chapter 6 when Reuven's father tells him about the history of Hasidism. A man named Israel spent time in the mountains thinking and meditating where he "gave birth to Hasidism". Later he came to be called Ba'al Shem Tov.