The South Korean, who served as leader in the U.N. from 2007 through 2016, will take over for Youssoupha Ndiaye.
In his acceptance speech Thursday, Ban called his new task "a serious responsibility."
Among his immediate tasks will be a vote-buying scandal involving last year's Olympics in Rio de Janeiro. A Brazilian IOC member, Carlos Nuzman , is under investigation for his alleged role in a $2 million vote-buying scheme to bring the games to Brazil.
Earlier this week, IOC president Thomas Bach said the committee was awaiting word from Brazilian authorities before determining next steps. One IOC member, Dick Pound, said the committee needs to act more decisively, and the ethics commission should be conducting its own investigation.
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