I'll nominate Luciano Vincenzoni who just died. Known as "the script doctor" he wrote and fixed somewhere around 70 films including Leone's For a Few Dollars More & The Good, the Bad and the Ugly, Wilder's Avanti!, Germi's Seduced & Abandoned, and even Schwarzenegger's Raw Deal. Seems like he hated a good chunk of his work, hung with William Holden, Kirk Douglas & Tony Curtis (there's a trio), and was generally badass.