Itchy is an antagonist in The Itchy & Scratchy Show, a parody of Tom & Jerry that play in The Simpsons world. He is a dangerous and sadistic mouse who loves torturing Scratchy, always killing him in some gruesome way in every episode.
In the show, Itchy is voiced by a parody of the late June Foray, outside of The Simpsons, he is voiced by Dan Castellenata, the same voice of Homer Simpson and many other characters in the show.
In The Simpsons Movie, a movie of Itchy & Scratchy is being played, where both Itchy and Scratchy are astronauts who reached the Moon. While Scratchy says he comes in peace for cats and mice everywhere, Itchy impales Scratchy with a flag pole several times whacks him with the pole and once Scratchy is down, Itchy cracks Scratchy's helmet, taking away his oxygen and leaves him on the Moon to die, while he goes back to Earth, lies to the public that he tried to rescue Scratchy although he did the opposite, and he ends up becoming president of USA. While looking into the Moon with a telescope, he sees Scratchy is still alive, threatening to tell everyone the truth. Itchy then shoots a salvo of rockets towards the Moon to kill Scratchy. Scratchy swallows the rockets and explodes.
Scratchy was at one point able to tie Itchy to several dynamite and Scratchy escaped in a taxi car. It is untold what actually happened, but according to a Simpsons book, it was said that Scratchy never killed Itchy even once although he nearly did, so it was especially possible that Itchy was able to survive the near-death experience.
He is the playable character in the video game based on Itchy & Scratchy.
While Itchy & Scratchy cartoons have elements of Tom & Jerry, the more brutal elements are derived from another more obscure cat & mouse cartoon series, Herman & Katnip.
In the comics based on Itchy & Scratchy, Itchy is if anything even more murderous and sadistic in tormenting Scratchy.