Complex sentence: Jim Hill was the legendary "empire builder", whose railroads-included the Great Northern Railway (U.S.), was a man given to notable rages when anyone dared to oppose one of his grandiose schemes.
Split into simpler sentences: Jim Hill was the legendary "empire builder", whose railroads included the Great Northern Railway (U.S.). He was a man given to notable rages when anyone dared to oppose one of his grandiose schemes.