Batman: Detective Comics # 36 "Professor Hugo Strange"

Detective Comics #27 (May 1939) featured the first appearance of Batman. That superhero would eventually become the star of the title, the cover logo of which is often written as "Detective Comics featuring Batman". Because of its significance, issue #27 is widely considered one of the most valuable comic books in existence, with one copy selling for $1,075,000 in a February 2010 auction.
Batman's origin is first revealed in a two-page story in issue #33 (November 1939). Batman became the main cover feature of the title beginning with issue #35 (January 1940). Issue #38 (April 1940) introduced Batman's sidekick Robin, billed as "The Sensational Character Find of 1940" on the cover and the first of several characters that would make up the "Batman Family". Robin's appearance and the subsequent increase in sales of the book soon led to the trend of superheroes and young sidekicks that characterize the era fans and historians call the Golden Age of Comic Books. Several of Batman's best known villains debuted in the pages of Detective Comics during this era including the Penguin in issue #58, Two-Face in issue #66, and the Riddler in issue #140.
Batwoman first appeared in Detective Comics #233 (July 1956) Since the family formula had proven very successful for the Superman franchise, editor Jack Schiff suggested to Batman creator, Bob Kane, that he create one for the Batman. A female was chosen first, to offset the charges made by Fredric Wertham that Batman and Robin were homosexual. Writer Bill Finger and artist Sheldon Moldoff introduced Bat-Mite in issue #267 (May 1956) and Clayface in #298 (December 1961).
In 1964, Julius Schwartz was made responsible for reviving the faded Batman titles. Writer John Broome and artist Carmine Infantino jettisoned the sillier aspects that had crept into the franchise such as Ace the Bathound and Bat-Mite and gave the character a "New Look" that premiered in Detective Comics #327 (May 1964). Schwartz, Gardner Fox, and Infantino introduced Barbara Gordon as a new version of Batgirl in a story titled "The Million Dollar Debut of Batgirl!" in issue #359 (January 1967)