He's been called String Wizard, and it suits him. He not only plays like a wizard, he even looks a little like Saruman the White. I think somebody else already snapped up Lord of the Strings, but that would be a good nickname, too.
The Nitty Gritty Dirt Band is one of the most venerable groups ever, but John has also performed in many other contexts. Working as a solo, John McEuen was the first person I ever heard play classical music on the 5-string banjo, years before Bela Fleck. I don't remember now what the piece was, only that it was intricate and beautiful.
Always a pioneer, John was one of the first prominent players to discover Shubb capos, and soon all his friends were using them. They began using my name with a lowercase "s", as a generic for capo ("hey, got an extra shubb?") On the inner jacket of Circle II, there's a closeup of a Shubb capo on a mandolin neck, vindicating mandolin capo users for all time.