In an undated photo via the Polak family, Dr Paul Polak with men operating a well-digging rig made largely of bamboo in Bangladesh in the 1980s. Polak, a former psychiatrist who became an entrepreneur and an inventor with a focus on helping the world’s poorest people create profitable small businesses, died on Oct 10 in Denver. He was 86. The New York Times

Social entrepreneur Paul Polak dies

The former psychiatrist and real-estate speculator turned to helping the poor make money by selling foot pumps, charcoal and clean water