Panama papers
I'm surprised no-one has made a thread on this yet. A Panamanian law firm called Mossack Fonseca has leaked over 11,5 million documents implicating much of the world's political class in off-shore banking and embezzlement. The leaked documents reveal information on the likes of Putin, David Cameron and FIFA. It has already led to Iceland's PM stepping down and has revealed among others that a British banker has aided North Korea in purchasing weapons.
The Guardian has a dossier on its website that features a large amount of articles on all the most important revelations concerning this huge data leak: