Dr. Hugo Strange (not to be confused with Marvel's Doctor Strange, or Nedor Comic's Doc Strange) appears in Detective Comics months before Batman #1 (the first appearance of the Joker and Catwoman). Dr. Hugo Strange is also very much like another early villainous doctor, Dr. Death. Their physical appearance, and their use of science to create weapons may lead one to question whether the two early characters are that much different. They appear six months apart and are nearly identical.
Strange originally operates as the leader of a gang, and uses science to create fog machines and super strong 15 foot mutant henchmen. He is also the first villain to deduce Batman's identity, and attempts to auction off the information.
Strange gets reinvented in the early '90s as a psychiatrist obsessed with the Batman, and tries to become the Dark Knight. In the Prey and Terror storylines, he works with the GCPD and is an advocate for an anti-Batman task force. He also pairs up with another insane psychiatrist, the Scarecrow. Everything backfires and Strange ends up in Arkham. This Batman obsession has recently become a theme every new (and sometimes old) villains have. Bane, the Court of Owls, Prometheus, Dr. Hurt, and Hush all have a Batman obsession that is the driving force behind their plots to kill or ruin the Batman. Even the Joker recently has fallen into this trope.
Dr Hugo Strange as psychiatrist has become the more popular version of the character, and often he is seen as a doctor at Arkham Asylum, but has also appeared at Belle Reeve, or in a private practice in Gotham. The Arkham connection is also shared by other doctor/psychiatrist characters like Harleen Quinnzel, Tommy Elliot, Jeremiah Arkham, and Jonathan Crane.
I always thought he was far more dangerous as a respected psychiatrist than as a crazy Batman-obsessed, kidnapper/gang leader. The video game Arkham City helped to recast Strange as a worthy Batman foe. A trusted doctor that studies people's minds and prescribes medication, and practices some ethically questionable studies on the human psyche can be a truly scary premise. Dr. Hugo Strange is definitely one of Batman's most underrated villains with so much potential.