Detective Comics #27 - First appearance of the Bat-Man and Commissioner Gordon
Detective Comics #29 - The Bat-Man meets Dr. Karl Hellfern, alias Dr. Death, the first Batman super-villain. The Bat-Man kills Hellfern's Indian henchman Jabah by snapping his neck with his silken rope. The first items from the utility belt: a vial of choking gas and suction cups that Batman uses to scale a building.
Detective Comics #30 - 1939 A rematch with Dr. Death and Batman kills another henchman, Mikhail.
Detective Comics #31 - First appearance of Bruce Wayne's fiancee Julie Madison, and of the Batarang and Bat-Gyro (the forerunner of the Batplane)
Detective Comics #33 - Bat-Man's origins are revealaed
Detective Comics #36 - Batman meets Professor Hugo Strange
Detective Comics #38 - First appearance of Robin
Detective Comics #48 - First references to the Batmobile and the Batcave
Detective Comics #58 - First appearance of the Penguin
Detective Comics #60 - First appearance of the Bat Signal
Detective Comics #66 - First appearance of Two-Face
Detective Comics #110 - The Bat-boat is introduced
Detective Comics #156 - Batman unveils a brand-new Batmobile
Detective Comics #168 - The Joker's origin is revealed for the first time
Detective Comics #233 - Kathy Kane becomes Batwoman
Detective Comics #235 - Batman encounters Lew Moxon, the man who hired Joey Chill to kill Thomas and Martha Wayne, and learns that Thomas Wayne was the first 'bat-man'
Detective Comics #250 - Batman battles an alien criminal
Detective Comics #257 - Introduction of the Whirly-Bat one-man helicopters
Detective Comics #267 - First appearance of Bat-Mite
Detective Comics #327 - Julius Schwartz takes over as Batman editor, ushering in the 'New Look.' Aliens, monsters, Bat-Mite, Batwoman, Bat-Girl, Bat-Hound, and Vicki Vale are banished; Batman gets a yellow circle on his chest emblem
Detective Comics #328 - Alfred is killed; Bruce Wayne starts the Alfred Foundation in his memory, and Aunt Harriet arrives at Wayne Manor
Detective Comics #334 - First appearance of the mysterious villain the Outsider
Detective Comics #347 - The 'Golden Age' Batman of Earth-Two appears for the first time (in an Imaginary Story)
Detective Comics #356 - The Outsider is revealed to be a revived Alfred, who's quickly restored to normal; the Alfred Foundation is renamed the Wayne Foundation
Detective Comics #359 - Barbara Gordon appears as the second Batgirl
Detective Comics #395 - First Batman story by Denny O'Neil and Neal Adams: "Secret of the Waiting Graves"
