Former President Clinton's birth certificate records William Jefferson Blythe Jr. (1918-1946) as the father. Blythe was indeed married to Clinton's mother. The difficulty is that he was serving in the United States Army at the time, and apparently was stationed in Europe when his alleged son would have been conceived. This is a conflict of dates that has never been resolved.
Do a web search for "President Clinton's real father", and you well see a number of discussions of this subject. It is all speculation, however, and would take a DNA study to verify.