“Grindelwald. You cannot imagine how his ideas caught me, Harry, inflamed me. Muggles forced i

“Grindelwald. You cannot imagine how his ideas caught me, Harry, inflamed me. Muggles forced into subservience. We wizards triumphant. Grindelwald and I, the glorious young leaders of the revolution. Oh, I had a few scruples. I assuaged my conscience with empty words. It would all be for the greater good, and any harm done would be repaid a hundredfold in benefits for wizards. Did I know, in my heart of hearts, what Gellert Grindelwald was? I think I did, but I closed my eyes. If the plans we were making came to fruition, all my dreams would come true.”

— Harry Potter and the Deathly Hallows 

Gellert Grindelwald