Professor Hugo Strange

Along with The Joker and Catwoman, Professor Hugo Strange was one of the villains appearing in Batman #1 (Spring 1940).
However, that wasn't his first confrontation with The Batman.

First appearance: Detective Comics #36 (cover-dated February 1940, but according to the GCD went on-sale December 30, 1939).





His second appearance was in Batman #1 ...






But that appearance really should have been in Detective Comics #38 (April 1940), based on the last page (last panel) of the Batman story in Detective Comics #37:

and if you look at the last panel of the Hugo Strange story in Batman #1,


The Hugo Strange story in Batman #1 also made no mention of Robin the Boy Wonder (who had appeared in the other Batman stories in Batman #1). And it was the introduction of Robin that was featured in Detective Comics #38 instead of the second Hugo Strange appearance.

From Who's Who: The Definitive Directory of the DC Universe Vol. XVIII (August 1986):

It looks like Hugo Strange made one other Golden Age appearance in Detective Comics #46 (December 1940)


And then it wasn't until 1977 before he was brought back?