Leslie Charteris began writing the books in 1928 and continued until 1963. The suave, wise-cracking Robin Hood figure caught the imagination of the American public, spawning movies (with the inimitable George Sanders), copycat movies (also with Sanders) , comic books, radio shows (superbly done by a young Vincent Price), and a popular T.V. series with Roger Moore. The regrettable 1997 film character (played by Val Kilmer) bears no resemblance to the original debonair protagonist.
Simon Templar (S.T. = saint) is a droll sophisticate who follows his own code. Like Zorro and the Scarlet Pimpernel he is a "good guy" who is on the wrong side of the law. His mix of worldliness, boyishness and good humor endeared him to gazillions of fans. Charteris describes him as a "flippant dandy with the heart of a crusader, a fighter who laughed as he fought, the reckless, smiling swashbuckler, the inspired and beloved leader of men..." (p. 123)
(Be forewarned that the books and films contain stereotypes that were common in the '30s and '40s.)