The hair says it all. He's certainly a one-off.
I remember him giving a recital at the Royal Festival Hall back in the 60s and being very impressed indeed with his Sinfonietta. I even went so far as to buy a copy, though I've never learnt it. It's not just that it's difficult (in those days I could probably have coped with that), but it definitely needs the right sort of organ - French or neo-classical, preferably both - something spiky and colourful like the music. I can't imagine it sounding nearly so gripping on the average English organ, though some of our larger instruments could no doubt cope.