"He was 86 and suffered a stroke a few months ago. He always said he didn't want to suffer and when the time came, he would be ready," said Stephen Viscusi.
Wilson, who began the hedge fund Wilson Associates with $15,000 and was later estimated to have earned $800 million, was described as witty, bright and very generous.
The Detroit native had no children and was divorced from his only wife, Marilyn, with whom he was married for 35 years, the New York Post reported Tuesday.
"His plan was to give all his money away. He told me recently, 'I only have about $100 million to go,'" said Viscusi.
He was a frequent benefactor to private Catholic schools and gave $100 million each several well-known organizations, such as the Nature Conservancy and the Environmental Defense Fund, the newspaper said.
"He was the most committed person I have ever known," said the president of World Monuments Fund Bonnie Burnham.
"More than his financial contributions, he brought an astute mind and sharp wit to the organization. He will be missed greatly and long remembered as a visionary donor," she said.
Wilson took his life by jumping from his 16th story apartment on Central Park West in Manhattan, the police said.