In the 1980s, Chuck Feeney was a hidden billionaire. As co-founder of Duty Free Shoppers, he had the wealth to live in castles and fly private jets. But his reality was very different. He lived in a modest rented apartment, carried papers in a plastic bag, and wore a simple Casio watch. Friends said he was happiest blending in, never showing signs of his immense fortune. Behind the scenes, Feeney was quietly giving it all away. In 1982, he launched Atlantic Philanthropies, and just two years later, transferred his entire stake in his company to fund it. Over the next four decades, he donated more than $8 billion — supporting…