Here are nine billionaire pledgers planning to give away most of their money, and how they plan to give.
Microsoft cofounder Paul Allen joined the Giving Pledge in 2010.
He focuses the majority of his philanthropic efforts within the Pacific Northwest, where he lives and works, particularly in the realm of science research.
initiatives and programs around the world that support agricultural development, emergency relief, urban poverty, global health, and education.
Later in his career, Gates pursued a number of philanthropic endeavors, donating large amounts of money to various charitable organizations and scientific research programs through the Bill & Melinda Gates Foundation, established in 2000.
The Gateses are particularly devoted to fighting diseases that, with treatments like vaccinations, are easily preventable.
Gates has one elder sister, Kristi (Kristianne), and one younger sister, Libby.
He is the fourth of his name in his family, but is known as William Gates III or "Trey" because his father had the "II" suffix.
Gates went on to create a fortune estimated at £35 billion and devote his life to philanthropy; Allen, whose accusations of foul play this month earned him the sobriquet 'the bitter billionaire' in the U. press, appeared to vanish completely and has spent the past 20 years as a Gatsby-esque recluse.
Unless you are a rock star who relishes playing at billionaires' birthday parties, a Hollywood actress in need of a free French mansion, or a supermodel looking for the ultimate yacht on which to sunbathe, you are unlikely to have even heard of Allen, the 'other man' in the Microsoft story.