Elliott Gould
Over the past 40 years or so, we've gotten used to seeing Elliott Gould large and in charge. From the original Trapper John in M*A*S*H to Philip Marlowe in The Long Goodbye to mobster Reuben Tishkoff in the Ocean's movies, Gould can be a pretty intimidating screen presence.
One of the great what-if stories in Hollywood history has Elvis Presley turning down the starring role opposite Barbra Streisand in A Star is Born.