Man of principle made riches in a way (10)
'man of principle' is the definition.
(I've seen this before)
'made riches in a way' is the wordplay.
'in a way' is an anagram indicator.
'maderiches' with letters rearranged gives 'ARCHIMEDES'.
(Other definitions for archimedes that I've seen before include "Old mathematician", "'Eureka' scientist", "Greek physicist", "Greek mathematician and inventor", "Greek mathematician ('Eureka')".)