Batman
The first Batman story, "The Case of the Chemical Syndicate", was published in "Detective Comics" #27 (May 1939). Finger said, "Batman was originally written in the style of the pulps", and this influence was evident with Batman showing little remorse over killing or maiming criminals. Batman proved a hit character, and he received his own solo title in 1940 while continuing to star in "Detective Comics". By that time, Detective Comics was the top-selling and most influential publisher in the industry; Batman and the company's other major hero, Superman, were the cornerstones of the company's success. The two characters were featured side-by-side as the stars of "World's Finest Comics", which was originally titled "World's Best Comics" when it debuted in fall 1940. Creators including Jerry Robinson and Dick Sprang also worked on the strips during this period.
Batman
The early, pulp-inflected portrayal of Batman started to soften in "Detective Comics" #38 (April 1940) with the introduction of Robin, Batman's junior counterpart. Robin was introduced, based on Finger's suggestion, because Batman needed a "Watson" with whom Batman could talk. Sales nearly doubled, despite Kane's preference for a solo Batman, and it sparked a proliferation of "kid sidekicks". The first issue of the solo spin-off series "Batman" was notable not only for introducing two of his most persistent enemies, the Joker and Catwoman, but for a story in which Batman shoots some monstrous giants to death. That story prompted editor Whitney Ellsworth to decree that the character could no longer kill or use a gun.