The Picasso of Bonsai
According to Will Hiltz, the author and publisher of Gnarly Branches, Ancient Trees, it was Frank Okimura who first referred to Dan Robinson as the Picasso of Bonsai. I think these photos and the photos in Gnarly Branches make a pretty good case for that name. Another title that fits is Dan is Bonsai Pioneer (also from Gnarly Branches, Ancient Trees).
The natural in naturalistic
The notion of naturalistic bonsai versus more stylized trees is a topic that has been kicking around in our bonsai world for a while now. In this light, a couple other names that might suit Dan Robinson are Mr. Natural, or the King of Naturalistic Bonsai (no offense to Walter Pall, who makes a strong case for whole notion of naturalistic bonsai and backs up his case up with some powerful trees).