Jon Lord of Deep Purple did for the Hammond B3 organ, what Eddie Van Halen did for electric guitar. He took what used to be thought of as a small church organ, hooked it up to a pile of 100 Watt Marshall amps and stacks of Leslie speakers. The results were, shall we say, impressive! :D

Lord and Ritchie Blackmore pioneered a lot of stereo-effect counterpoint harmonies played live. And they were into classical music long before Malmsteen et al were even heard of!

Most people think of the albums released during their peak period (Fireball, Machine Head) but I recommend checking out early stuff like Book Of Taleisyn and Purple Passages as well. A lot of the stuff that's out now seems like a weak echo of things that happened 35 years ago.