Harry Potter: 15 Most Powerful Wizards In The Wizarding World
2. Gellert Grindelwald
While there are some who will call Voldemort the Hitler of the wizarding world, that rather clumsy label actually belongs more pertinently to Gellert Grindelwald, a nefarious murderer far more intent on the destruction or subjugation of inferior Muggles than on forwarding his own mythology.
He started early, earning himself an expulsion from Durmstrang where he had built a reputation as one of their most gifted students ever, when his twisted experiment came to light. He applied his genius level intellect to furthering his magical knowledge and mastering it practically, mastering almost unprecedented skills like rendering himself invisible without the use of an Invisibility Cloak or exploding enemies with a mere slash of his wand.
As his time in disguise as Percival Graves also proved he was a gifted Occlumens, able to trick even the top level wizards at the MACUSA, where he ascended to a top position in Magical Law Enforcement, presumably meaning he'd shown considerable aptitude for traditional Defence Against The Dark Arts magic. In other words he was the real deal.