He could make a much bigger difference if he simply saved a large portion of his earnings over his career, invested them (if he's working for a hedge fund he should be able to get a great return), and then invested that much larger chunk into 3rd world entrepreneurs/businesses.

The unfortunate truth is that most money that goes into charities that operate in 3rd world countries gets spent on logistics, bureaucracy, and gets siphoned off by corrupt governments or stolen by thieves. He'll save someone from malaria one day, and they'll die from another cause later.

A much bigger impact would be to invest in those 3rd world countries (conscientiously), and provide jobs and livelihoods for those people. Build infrastructure, enable access to capital, machinery and technology, security, etc... That will make a much larger difference than any amount of money poured into charities and feel-good causes.