Katnip was the primary antagonist in the feature cartoon series Herman & Katnip, nowadays usually shown in syndication with Casper and Baby Huey cartoons. An extremely dimwitted cat, he was always bested (without exception) by his nemesis Herman, a mouse who was portrayed as kind of streetwise Mighty Mouse, though he was neither as strong or moral as him, nor was he as clever as Jerry. Katnip would frequently be led straight into the schemes of Herman (who, despite always winning, was not always the good guy). The level of brutality and cruelty Herman would enact on Katnip often pushed the limits of even that slapstick, pre-PC era of cartoons. Matt Groening has even said that Itchy & Scratchy are based far more on Herman & Katnip than on Tom & Jerry
Herman could be cruel to Katnip, but Katnip wasn't innocent either. On the rare occasions he had Herman cornered, he thoroughly enjoyed his brief advantage. Katnip's own cruelty surfaced in the sequence of the cartoons before Herman arrived - the premise usually had him away for some reason - when all Katnip had to face were the common mice, who while not as dimwitted as the cat, were also nowhere near as clever as Herman, and prone to enacting scams that often put them right in Katnip's sights. Herman and the other mice were modeled somewhat after the lovable film losers, The Bowery Boys, and spoke with classic Brooklyn-Queens accents, ala Bugs Bunny. While able to briefly get the better of Katnip, the other mice served the purpose of running from him, calling for Herman to get them out of their latest jam, and then aiding and sometimes screwing up Herman's efforts to strike back at Katnip. The closest Katnip came to getting back at the mice was as an unseen presence/menace at the start of a cartoon; Each mouse that went to face him was quickly after seen as a ghost/angel floating away and waving goodbye.
Katnip spoke in a classic dullard's voice, very similar to Baby Huey done by the same actor. He is also unique even for his era in another respect. One cartoon, the mice tricked Katnip into believing he was dead, in the afterlife and facing an eternity of 'da fiery furnace' - which could be avoided only if he served the mice back on Earth. While not brought up by name due to the era, few antagonists had their opponent deliberately threaten to send them to Hell.