Bonus: King George V of Great Britain
A King of Great Britain is not the first person you would think of as a major drug fiend. The crusty old monarch was chronically ill with lung disease for several years, but his death is believed to have been accelerated when his personal physician, Lord Dawson of Penn, stupidly gave him a mixed dose of cocaine and morphine. This man is definitely a contrast with the other people in this list (for one thing, being a royal, he had no discernible talent!), but it just goes to show that, even in the 1930s, speedballing was a problem.