Ranking second was the late John Santikos, who built the largest family-owned theater chain in Texas. Santikos gave $605 million from his estate to the San Antonio Area Community Foundation.
Ranking third was Michael Bloomberg, whose giving in 2015 totaled $510 million. He was followed by New York hedge-funder John Paulson, who gave $400 million to Harvard University. EBay founder Pierre Omidyar came in fifth and was the top-ranked tech giver on the list, with $327 million in giving.
Other notables included the Walton family, with founder Sam Walton's three children giving $407 million in Wal-Mart stock. The Gateses gave $272 million to their foundation, while 48-year-old entrepreneur Jay Faison, who founded SnapAV, gave $165.6 million to promote clean energy. Warren Buffett's sister, Roberta Buffett Elliott, gave $100.9 million to Northwestern University.
The 23 billionaires on the list gave an average of less than 1 percent of their estimated wealth. Of the 23, former hedge-fund manager John Arnold and his wife, Laura, gave the largest share of their fortune, at 5.6 percent.
The top 50 list only measures one year, so many donors, such as Gates, are giving away far more of their fortunes over longer periods of time. Whereas the Gates family donated just 0.4 percent of their $76 billion wealth last year, they've gifted $1 billion or more to their foundation several times.