Killer Moth makes the cover of Batman 63 (Feb/March 1951) for his first appearance.
The Joker also appears in this issue, in a story by Finger, Sprang and Paris, which sees him adopt a variety of disguises.
The Joker attends an exhibit of Batman’s various outfits, and gets inspired to create some alternate costumes of his own. Although, unlike the suits that Batman creates, these do not have distinct attributes for crime fighting.
Instead, they largely function as disguises to set up his crimes. The costumes are all based on “humourous” figures from fiction, such as Falstaff and Old King Cole.
Still, the story plays out well, and moves from great scene to great scene. There is even a giant penny in one sequence. Perhaps Batman loaned it out.
Cameron Van Cleer, the Killer Moth, is introduced in this story Finger, Schwartz and Paris.
Van Cleer is a part of wealthy Gotham society, and keeps his criminal identity a secret, making him somewhat a re-working of the Cavalier. But he also creates his own Moth-cave and Mothmobile, and hires himself out as a helper to criminals in need, to be summoned with a Moth-Signal. So this story also takes off on the Joker one from a few years earlier, in which he did much the same thing.
Killer Moth proves a big challenge for Batman, as his Mothmobile is able to outperform even the new Batmobile.
We also see that the antennae on his helmet are not merely decorative, but allow him to overhear messages relayed between Batman and Robin. Killer Moth escapes from Batman at the end of the story, and keeps his secret identity intact.
Killer Moth returns in the next issue.