I'm feeling a bit lazy tonight, so I'm going to let Wikipedia do a little bit of my work for me:
"The original Killer Moth is a prisoner identified only by his prison number, 234026. While in prison, he reads a newspaper article about Batman and decides to set himself up as the "anti-Batman," hiring himself out to Gotham City's criminals to help them elude capture by police. Upon his release, he uses the hidden proceeds of his crimes to build a "Mothcave", modeled on the photos of the Batcave in the newspaper article he read.
Killer Moth also establishes a false identity, as millionaire philanthropist Cameron van Cleer. In this guise, he becomes friends with Bruce Wayne. Meanwhile, he promotes himself to Gotham's criminals using his identity as Killer Moth, giving them each an infra-red Moth-signal. In his first job, he rescues some criminals from the police and then uses his Mothmobile to defeat and capture Batman and Robin. The duo escape and lead Killer Moth to a climactic battle on Gotham Bridge, which ends when the villain plunges 1,000 feet into the river and disappears.
In his second appearance (Batman #64 March 1951) Killer Moth kidnaps Bruce Wayne and learns his secret identity. However, he is shot by other criminals and the resultant cranial injury causes amnesia. He remains a persistent enemy appearing through the Silver Age of comics. He is frequently remembered as being the first criminal Batgirl encounters in Detective Comics #359. "
So basically, this guy dresses up as a MOTH and hires himself out to crooks as an anti-Batman. A moth. You know what bats eat? Moths. You know how stupid moths are? They're so stupid they think your porch light is the sun and yearn to be near it. There are so many tougher animals, even tougher insects this guy could have been. And that costume is so... garish. It's just sad. I take back every mean thing I said about Sinestro, Black Manta and Brainiac. Killer Moth, you just suck. I hope you get eaten by Man-bat.