Complex sentence: William Avery Rockefeller, Jr. (May 31,1841--June 24,1922) was an American financier who co-founded Standard Oil with his older brother John Davison Rockefeller (1839--1937).
Split into simpler sentences: William Avery Rockefeller, Jr. (May 31,1841--June 24,1922) was an American businessman and financier. He was a co-founder of Standard Oil along with his older brother John Davison Rockefeller (1839--1937).