Earth-Forty

Reality names were reused several times. See also Earth 40, Earth-40.

History

Earth-Forty is an alternate universe, first described in Crisis on Infinite Earths: The Compendium.

It is inhabited by a Captain Thunder whose real identity was Billy Batson and variants of some Earth-One and Earth-Two characters.

Other defining characteristics are:

Superboy was raised in Metropolis
Wonder Woman fought in WWII and had adventures similar to her Earth-Two counterpart.
Bruce Wayne retired by the mid 1960's to make way for a new Batman and Robin Team.

Crisis on Infinite Earths: The Compendium stated that the following stories/comics were appearances of Earth-Forty:

Crisis on Infinite Earths: The Compendium lists entire issues rather than specific stories, leaving the question if any non contradictory stories in those issues occurred on Earth-One, Earth-Forty, or both.
The Compendium lists Thrill Comics #1 (1940) as happening on Earth-Forty but doesn't count it as a first appearance (possibly because it was an ashcan comic)
The Compendium also doesn't count the 1943 Batman newspaper strip as a first appearance of Earth-Forty either (possibly because it wasn't an actual comic book).
The Crisis on Infinite Earths: The Compendium stated this was "revealed as a distinct parallel Earth in The Kingdom #2" making this reality part of hypertime.
Queen Hippolyta is depicted as a blond in The Legend of Wonder Woman 1–4 rather than having brown hair as on Earth-Two.
The Essential Wonder Woman Encyclopedia (2010) doesn't list Earth-Forty and assigns the "Golden Age" Wonder Woman stories to Earth-One resulting in those stories happening with variation on all three Earths.

If one counts Thrill Comics #1 (1940) as Earth-Forty's true first appearance and Convergence #0's implication that Earth-Two didn't appear until The Flash #123 then it is one of the three oldest alternate realities officially identified (the other two are Earth-Two-A and Earth-Quality). In any case Earth-Forty is the oldest official hypertime reality.