How did they entice so many big stars into playing villains on the old Batman TV show?
Seems hard to picture four decades later, but a show like Batman could introduce a star to a new audience. Most of the folks you mentioned (Meredith, Romero, etc.) were already doing shows like Bonanza, Please Don’t Eat The Daisies, Ben Casey, The Man From U.N.C.L.E. and so on. When most American households were limited to only a few channels and Hollywood churned out fewer movies, this is how those folks kept up a certain standard of living. According to imdb, Meredith appeared in a total of 20 episodes — the most frequent of the villains. It’s probably also important to remember that Superman (the tv show) had done well in the ratings, and that Batman (the character) was almost as iconic. There was also a big screen version of Batman that did reasonably well at the box office and got those big stars in an ensemble piece similar to It’s A Mad, Mad, Mad World. Besides the constant attention the villains got, they also won acclaim. Frank Gorshin was nominated for an Emmy Award as The R