William P. Bengen's paper appeared in the Journal of Financial Planning
http://www.retailinvestor.org/pdf/Bengen1.pdf
This was the first time a "safe" withdrawal rate of 4% was calculated for a 30 year retiree with a mix of stocks and bonds. The Trinity Study and on-line tools like Firecal that came along later, made it possible for thousands of people to do realistic retirement planning.
I think my first encounter with "4% rule" was when I read an a column in the Dallas Morning News by the financial columnist Scott Burns, or was it in (the now defunct) Worth magazine? He was taking on legendary investor Peter Lynch, manager of Fidelity Magellan Fund, who had said you could withdraw the market average real return of 7% per year.
Happy birthday Bill and thanks!