On Seinfeld, the three other main characters will often ask for Kramer's opinion and get one that usually defies social norms. Sometimes they don't even ask and he will still offer such an opinion.
His opinions come from an unfiltered and brutally honest place. Such examples are:
George's girlfriend has a large nose. The whole gang is in Jerry's apartment and are being polite, telling her that she doesn't need to do anything with her nose. Kramer busts in the apartment and immediately tells her to get a nose job (with gusto).
Elaine opens a Christmas gift from George, who bought her a cashmere sweater marked down to $85 from $600 because of a barely discernible red dot. Kramer looks at the sweater and in the same moment alerts Elaine to the red dot.
The gang are trying to dissuade Wendy Malick's physical therapist character from her outrageous beehive hairdo (without letting her know it is tacky). They plan for Kramer to come in and to act with this reckless honesty, only to have him tell Malick that her hair is great, that no-one wears it like that anymore.
George uses Jerry's phone number as a contact number for his fraudulent latex sales business. While George is using his bathroom, Kramer enters Jerry's apartment, answers the phone and says there's no Van deLay here, ('you're way off').
Kramer, upon seeing Frank Costanza's bare chest, lets Frank know he has breasts. This leads to the invention of the manssiere. (AKA the bro)
What is the name or classification for this type of character in story development, whose honesty typically counters the will of the rest of the main characters?