The [Broadway] musical was ceaselessly protean in these years, usually conventional but always developing convention, twisting it, replacing it.
-- Ethan Mordden, Coming Up Roses
Roosevelt's performance in the civil rights meeting illustrated one of the central operating principles of his protean executive style, a style that transformed the presidency, and the nation: a willingness to delay decisions, change his mind, keep his options open, avoid commitments, or even deceive people in the relentless pursuit of noble objectives.
-- William Doyle, Inside the Oval Office
He was a protean character who constantly adapted to his environment.
-- David Maraniss, The Clinton Enigma
Protean is derived from Proteus, an ancient Greek god who had the ability to change his shape at will.