Warren Buffett and Bill Gates have been among the richest people in the world for many years. They used to trade places regularly as Number 1 and Number 2 of the most wealthy people on the planet. Although they have been passed up by others in the rankings, they still each have over one billion dollars.
Buffett and Gates started a pledge among fellow billionaires to give away most of their fortune by the time they die. They have gotten some other billionaires to join them in that endeavor.
There are many people in the world who are multimillionaires but not billionaires. They control so much money that they could do a lot of good by giving more of it away.