See update below.
I’m not sure if there is a proper word for these characters, so I’m calling them “sub-verbal” which means any character who speaks in gibberish. The Tasmanian Devil is probably the most well known cartoon character to sound this way. He was occasionally able to get out some English, but is generally known for his animal sounds.
Another of the great sub-verbal characters is the Muppet, “Swedish Chef”. Throughout his faux-swedish, he would pepper in some understandable English. I believe he now works as a writer for Ikea catalogs.
But one sub-verbal character that is on his way to being forgotten is “White Fang” from the Soupy Sales show. White Fang and Black Tooth were both supposed to be dogs, but all you see are their “arms” which reach into the scene. White Fang is very argumentative, and very entertaining.
And this gem featuring Alice Cooper.
UPDATE: I have recently learned term “grammelot” which wikipedia describes so:
Grammelot is a term for a style of language in satirical theatre, a gibberish with macaronic and onomatopoeic elements, used in association with pantomime and mimicry.
The format dates back to the 16th century Commedia dell’arte, and some claim Grammelot to be a specific universal language (akin to Lingua franca) devised to give performers safety from censorship and appeal whatever the dialect of the audience.
(Macaronic, btw, refers to text spoken or written using a mixture of languages)
Here is the video that introduced me to grammelot.