Bill Gates and the Gates Foundation will probably eradicate polio.
Before people jump on the bandwagon about how Gates is evil and problematic, that there are no virtuous billionaires, and a government or an NGO or an equivalent should have been the one to do it… I know. But the question was “name one billionaire that’s done anything good,” and I think it’s pretty difficult to argue that eradicating polio isn’t good.