Gary Keller is an American entrepreneur and best-selling author. He is the founder and Executive Chairman of Keller Williams, which is the largest real estate company in the world by agent count and second in closed sales volume, and units sold. Keller founded Keller Williams on training and education and later brought his teachings to print. His books include The Millionaire Real Estate Agent, The Millionaire Real Estate Investor, and The ONE Thing. He is considered one of the most influential people in real estate.

The One Thing: The Surprisingly Simple Truth Behind Extraordinary Results is a non-fiction self-help book written by authors and real estate entrepreneurs Gary W. Keller and Jay Papasan. The book discusses the value of simplifying one's workload by focusing on the one most important task in any given project. The book has appeared on the bestseller lists of The New York Times, The Wall Street Journal, USA Today, and Amazon.com. It was first published by Bard Press on April 1, 2013.