Steve Fossett achieved some serious aviation milestones, no doubt about it. However, "great aviators" don't fly in IMC (instrument meteorological conditions) with no instruments and no instrument rating.

Steve Fossett had an instrument rating, various jet type ratings as well as balloon and sailplane ratings. I wouldn't go so far as to call him the greatest aviator in the world but he was a very good one - setting dozens of world records in balloons, gliders, and powered flight.

Even very good aviators can make a critical mistake that kills them. For example, Frank Tallman was the top Hollywood stunt pilot for many years following the death of his partner Paul Mantz. Tallman died in a CFIT accident (controlled flight into terrain) when his plane struck a mountain on a routine flight. Scott Crossfield was truly a great aviator in anyone's book but he died when his 1961 Cessna 210 broke up at night in a thunderstorm. A readily available $2000 Garmin handheld GPS with weather receiver would've probably saved his life.