When David Ludlow's wife died in a climbing accident 11 years ago, her death transformed him into a multimillionaire: He inherited Vanda Sendzimir's share of her family fortune, a $5 million trust that generates an annual interest of about $300,000. Then a freelance photographer with a passion for social justice issues, the Jamaica Plain man was plunged into a swirl of shock, guilt, and confusion. I've always been very left-wing politically and all of a sudden I was living incredible inequality," said Ludlow, 64. "Suddenly I was in the upper 1 percent of the population in terms of wealth, and I felt terrible about that for a long time." So he did something radical, and something that many people might consider insane: He decided to give away half his annual income. In doing so, Ludlow joined a small, unusual, and growing community: The 50% League, an Arlington-based group of people who contribute at least half their income, business profits, or net worth to charity. Members from across the country have been welcomed into an elite circle of givers and asked to share their stories publicly, even if anonymously, to inspire other givers. Their motivations are manifold: Some give out of a sense of fairness, personal satisfaction or a desire for simplicity; others are driven by religious faith or dedication to a cause. Many are anonymous philanthropists, and not all of them have great wealth: Some are members of the middle class, but have chosen to survive on less so they can give more. Above all, they aim to stand as role models, and to encourage others of all income levels to think about their giving potential. "I feel incredibly privileged, and I still feel guilty about that," said Ludlow, who has used much of the money he inherited from his late wife ... to fund grass-roots groups led by low-income people of color. "But it's given me tremendous meaning in my life to give as much as I can away."