Complex sentence: He was a member of the "Rat Pack" and brother-in-law to President John F. Kennedy, and more noted in later years for his off-screen activities as a celebrity than for his acting.
Split into simpler sentences: He was a member of the "Rat Pack" and brother-in-law to President John F. Kennedy. In later years he was noted more for his off-screen activities as a celebrity than for his acting.