By early 1940, Kane and Finger discussed adding a sidekick. Robinson suggested the name "Robin" after Robin Hood books he had read during boyhood, saying (in a 2005 interview) that he was inspired by one book's N.C. Wyeth illustrations. The new character, orphaned circus performer Dick Grayson, came to live with Bruce Wayne (Batman) as his young ward in Detective Comics #38 (April 1940). Robin would inspire many similar sidekicks throughout the remainder of the Golden Age of Comic Books.
Batman's archnemesis the Joker was introduced around the same time, in Batman #1 (Spring 1940). Though Kane claimed he and writer Bill Finger came up with the idea for the Joker, most comic historians credit Robinson for the iconic villain, modeled after Conrad Veidt in the 1928 movie, The Man Who Laughs.