Question: Geoffrey G. Butler is the uncle and mentor of a man who was a prominent what? 
Sentence (from "Rab Butler"): Richard Austen Butler, Baron Butler of Saffron Walden, (9 December 1902 – 8 March 1982), generally known as R. A. Butler and familiarly known from his initials as Rab, was a prominent British Conservative politician. "
Relevant evidence: Yes