Emerson was the first rock musician to use a synthesizer (the Moog, being the first and only at the time)..

I'm sorry, michaelr, but that's nonsense.

Emerson first used a Moog at The Nice's Royal Festival Hall concert in February 1970. It had been used in 'rock' many times prior to this.

Some better known earlier albums featuring it (there are lots more):

1967 The Doors – Strange Days

1967 The Rolling Stones – Their Satanic Majesties Request

1968 The Byrds – The Notorious Byrd Brothers

1968 Simon and Garfunkel – Bookends

1969 The Beatles – Abbey Road

1969 Bread – Bread