Gary Keller is the founder and chairman of the board of Keller Williams Realty, Inc., one of the largest and most successful realty companies in the world. Keller was born in Texas into a family of teachers. Early on, he had a great interest in music and planned to make a career in that field. However, he decided he needed a college education and was surprised to find out that his parents had already sent in an application to Baylor University for him. At Baylor, Keller became interested in studying real estate. He worked as a real estate agent after college, eventually founding the company Keller Williams Realty, Inc. with partner Joe Williams.

Keller grew the company rapidly by putting principles laid out in The ONE Thing into practice. However, he achieved this success only by first struggling. In his book, he describes how he once believed he was failing: Keller felt burnt out and thought that his management techniques were not conducive to success. Over time, Keller realized that focusing, prioritizing, and discovering purpose were key to achieving success and fulfilment. This realization came with major changes—including ending his role as CEO of Keller Williams.