Who is the most underrated prog-rock keyboardist?

I'd like to nominate Józef Skrzek from SBB.

What are your candidates?

Falk Ulrich Rogner ... in the earlier days of AD2. Most incredible sound addition to the band, had personality and touch, and was able to also improvise very cleanly.

Like any other intelligent enough person I am always very sensitive and careful about terms like "underrated". I know what "overrated" might mean, but the opposite tip is sure controversial. Rolling Stones the band are no doubt overrated. KISS are terribly overrated. 

You do not really need to be into music theory and practice, to get why Kerry was one of a kind. Both in theory and practical implementation. Triplets and syncopations galore. Style so unique and distinguishable. 

Cressida had talented keyboards - Peter Jennings, they say. 

Greenslade - obvious candidate. To my ear of a music gourmand, not gourmet (as far as I know there are three grades of eaters: gluttons that just love to eat, gourmands that loves to eat delicious food, and gourmets that love exquisite food), Greenslade is step above ELP. Unique melodies, compact enough compositions. 

Fantasy (of Paint A Picture fame) and Spring (3 keyboardists, they say) had fine composers and performers. 

Ton Scherpenzeel. Kayak don't get a lot of love but they didn't record and release 18 studio albums for nothing. Ton played on all of them and was also the main writer. Tremendous player with Rick Wakeman like chops as evidenced by the track Royal Bed Bouncer.

Also Par Lindh is surely worth a mention.