The story goes that legendary stride pianist Fats Waller said the above about equally legendary jazz pianist Art Tatum when Tatum arrived at the club where Waller was playing. The compliment must have been doubly felt as Waller was something of an idol for Tatum.

Tatum is considered by many to be Waller's successor, blending his predecessor's brilliant stride work with his own gift for improvisation and unbelievable manual dexterity. (Charlie Parker once said he wished he could play like Tatum's right hand. But that's another story.) Both men were extraordinary musicians, but a good listen to Tatum will show you why Waller was so admiring. Try his famous 1933 recording of Tea for Two for starters and prepare to be amazed.
My father, who told me this story when I was very small.