The prime minister of Iceland, Sigmunder Gunnlaugsson, resigned Tuesday. On Monday, thousands of protesters had gathered outside the Icelandic Parliament to call for his resignation. The opposition grew after a report that he and other world political and business leaders used their power and wealth to avoid paying taxes. The group Consortium of Investigative Journalists looked at 11 million documents belonging to Mossack Fonseca, a law firm in Panama. The firm helps companies and wealthy people set up foreign businesses to avoid paying taxes. A computer hacker got the documents from the firm’s network. The reporters found nearly 130 current and former government leaders across the world, wealthy business owners, performers and sports stars used the Panamanian law firm to avoid paying taxes. One report said a musician friend of Russian President Vladimir Putin had accounts with the law firm. The musician’s name is Sergei Roldugin.