Not many facts were known about Pythagoras, and most stuff we know today is full of speculation. He was sort of a self-proclaimed math-loving cult-running messiah who loved math and Astronomy.
He set up a commune in italy where around 300 philosophers joined to live the life of restriction with him as their leader. The people living there were investing all of their time into studying Math, Astronomy and Music, as they believed that understanding these equals to understanding the universe. The members of the commune believed in reincarnation, so they didn't eat meat (this chicken could be your passed relative, why'd you want to eat that?).
Pythagoras presented himself as a demigod and has this cult-leader vibe around him when you think about it, but the thing to remember is that he didn't care about money, power and glory - he did it all for the love of science. The only reason why believed himself to be a messiah is that he possesed a knowledge which is so engrained into the universe that he really did feel all-powerful. It's impressive that here we are talking about something which every kid today learns in pre-algebra class.
Numbers have their representation everywhere in the universe, and figuring out that things like music are also governed by numbers (Law of Octaves) reinforces idea that Math is the ultimate way of figuring out how universe functions.
"Understanding of eternal facts is the closest man can get to being immortal."