Quiz about Scentists

I was an ancient Greek mathematician and mystic. I had a colorful, if somewhat obscure, early life in the eastern Mediterranean before I founded a religious and philosophical society in Croton based around mathematics. I swore all of my followers to strict secrecy, so it SHOCKS me that anything leaked out. Now everyone knows me for a little theorem about right triangles. I didn't even discover it; the Babylonians beat me to it by 1000 years. Who am I?