Complex sentence: His freewheeling abstract paintings set influential precedents for many younger American painters of the sixties, making him an important forerunner of American Lyrical Abstraction of the 1960's and 1970's.
Split into simpler sentences: His freewheeling abstract paintings set influential precedents for many younger American painters of the sixties. He is an important forerunner of American Lyrical Abstraction of the 1960's and 1970's.