William Clement Stone was an American businessman, philanthropist and New Thought self-help book author.

Stone was born in Chicago, Illinois, on May 4, 1902. His father died in 1905 leaving his family in debt. In 1908 he hawked newspapers on the South Side of Chicago while his mother worked as a dressmaker. By 1915 he owned his own newsstand. In 1918 he moved to Detroit to sell casualty insurance for his mother.

Stone dropped out of high school to sell insurance full-time. He received a diploma from the YMCA Central High School in Chicago. He took courses at Detroit College of Law (now, Michigan State University College of Law) and Northwestern University. Much of what is known about Stone comes from his autobiography The Success System That Never Fails. In that book, he tells of his early business life, which started with selling newspapers in restaurants. At the time, this was a novel thing to do, a departure from the typical practice of boys hawking newspapers on street corners.

At first, restaurant managers of restaurants tried to discourage him, but he gradually won them over by his politeness, charm, persistence and the fact that most restaurant patrons had no objection to this new way of selling papers. In 1919, he graduated to selling insurance policies in downtown business offices. His mother managed his new career. Then in 1922, he opened his own small insurance agency, Combined Registry Company, in Chicago. By 1930, he had over 1000 agents selling insurance for him across the United States.

In 1947, after his business had grown significantly, Stone built the Combined Insurance Company of America, which provided both accident and health insurance coverage. By 1979, his insurance company exceeded $1 billion in assets. Combined later merged with the Ryan Insurance Group to form Aon Corporation in 1987, and Combined was later spun off by Aon to ACE Limited in April 2008 for $2.56 billion.

Stone considered his success to be an example of the rags-to-riches protagonists in the Horatio Alger's stories he admired. He mentored Og Mandino, an alcoholic who became the Executive Editor of Success Unlimited Magazine.

In 1951, Stone founded the interfaith group "The Washington Pilgrimage", which later became the "Religious Heritage of America". It successfully advocated the Eisenhower administration to add the "under God" to the Pledge of Allegiance. Stone contributed up to $10 million to President Richard Nixon's election campaigns in 1968 and 1972; they were cited in Congressional debates after the Watergate scandal to institute campaign spending limits.

Stone emphasized using a "positive mental attitude" to succeed. Stone adopted the motto of his mentor, Napoleon Hill, "Whatever the mind can conceive and believe, the mind can achieve (with PMA)." In 1960, Stone teamed up with Napoleon Hill to author Success Through a Positive Mental Attitude. The book Success Through a Positive Mental Attitude includes the following testimonial from the Rev. Robert H. Schuller on the inside front cover page: "Success Through A Positive Mental Attitude is one of the ten books that has most impacted my faith and my philosophy...no person's education is complete without the concepts articulated in it so wisely and so well." Norman Vincent Peale said that Stone and Hill "have the rare gift of inspiring and helping people...In fact, I owe them both a personal debt of gratitude for the helpful guidance I have received from their writings." Stone and Hill also founded a monthly digest magazine, entitled Success Unlimited. In 1962, Stone wrote the Success System That Never Fails, in which he suggested how to become successful and have a healthy, productive lifestyle. In 1964, he and Norma Lee Browning collaborated on writing The Other Side of the Mind.