In the latest issue of Forbes Magazine, Validea CEO John Reese takes a look at one of investing history’s most unassuming stock market gurus, Joseph  Piotroski.

Piotroski, Reese writes, isn’t a slick, smooth-talking hotshot like Gordon Gekko (Michael Douglas’s Wall Street character). Instead, he’s a college accounting professor. But, Reese adds, Piotroski has had more of an impact on the investing world than many better-known pundits.

Back in 2000, while teaching at the University of Chicago, Piotroski authored a paper entitled “Value Investing: The Use of Historical Financial Statement Information to Separate Winners from Losers.” In it he detailed a step-by-step, accounting-based method to buy and short stocks that he found would have produced a 23% annualized return (before trading costs) from 1976 to 1996, more than double the S&P 500’s return.

Reese discusses Piotroski’s method, and the Guru Strategy computer model that Reese has developed based on Piotroski’s paper. A 10-stock portfolio of stocks picked with the model is beating the market by more than 4 percentage points since its February 2004 inception, and it’s been his best performer this year, holding a double-digit lead over the S&P 500 so far in 2010.

To read about Piotroski’s method, and to see a few stocks that Reese’s Piotroski-inspired strategy is high on, click here to read the full article.