Complex sentence: He and his four brothers established the Rockefeller Brothers Fund, a philanthropy, in 1940, where he served as Trustee, 1940--1975 and 1977--1979, and as President in 1956.
Split into simpler sentences: He and his four brothers established the Rockefeller Brothers Fund, a philanthropy, in 1940. He served as trustee, 1940--1975 and 1977--1979, and as president in 1956.