Mark Breland. Check out his amateur career. http://boxrec.com/media/index.php/Mark_Breland#Amateur_Highlights
He never won an olympic gold medal. But Courage Tsabalala had a record of 72-1 (72 Stops) in ams. All in the 1st.
Andre Ward 115-5 as an amatuer. Didnt lose an Am fight for 6 years before retiring with a gold medal at the olympics.
Donald Curry was I think the greatest Amateur fighter of all time but He missed the Olympics since the U.S. boycotted.