Professor Moliarity was a diminutive mole who tried to block out the sun using his invention, the Kineto Beam, which would effectively plunge St. Canard into eternal night and allow his entire race to storm the surface and conquer the city. He was stopped by Darkwing Duck, who destroyed the Kineto Beam and sent Moliarty and his fellow moles scurrying back underground where they came from.
In trying to evade Darkwing during a future encounter, Moliarty dug straight through the planet and ended up in Kung Pow City. The Masked Mallard followed him anyway and Moliarty was finally caught and turned over to the authorities in Kung Pow.
Moliarty holds the distinction as being the very first enemy Darkwing Duck ever faced if one is to take episode airdates into account. His first episode, "That Sinking Feeling", premiered during the series' spring preview on the Disney Channel, and later became the first episode to make its non-premium debut on ABC. This episode had the distinction of being the first one written and recorded so, despite being 5th in production number, it's truly the very first episode.
Moliarty, unfortunately, never ended up becoming a very popular character, only appearing twice more in the show's run, in "Aduckyphobia" (another spring preview episode) and a brief appearance at the beginning of "Kung Fooled" (which aired late in the syndicated run). In the comics, his only appearances were "The Kitty Kat Kaper" (Disney Adventures Volume 2, Number 9), "The Ballot of Darkwing Duck and Launchpad, Part 1" (Darkwing Duck #15), and a cameo in the DuckTales arc "Rightful Owners". Despite his very few appearances on the show, he also appeared in both of the Darkwing Duck video games.