William J. O'Neil is an American entrepreneur and stock trader, best known for founding the investment research firm Investor's Business Daily. He developed the CAN SLIM strategy, which combines fundamental and technical analysis to help investors identify growth stocks. O'Neil is also an author, having written several books on investing, including "How to Make Money in Stocks." His work has influenced many investors and traders, emphasizing the importance of market timing and stock selection based on earnings growth and price performance.