Simpsons brother - "we will never speak of him again"?

Question

Years ago in the Simpsons, a mention was made of an uncle - a brother of Marge's I think. Marge said a little bit about him, it wasn't a pleasant story, and she finished with "and we will never speak of him again" - and they never have, as far as I know.

I searched through all of the info on the Wikipedia, including the specific "characters" page, and couldn't find the answer.

Does anyone know who this relative was?

Chel - thanks for the info. However, the info on the Simpsons Wikipedia page in your link doesn't quite match the text you posted. Here is what I see for "Uncle Arthur" on that page:

Uncle Arthur is Bart's uncle. Therefore, he would be either Marge or Homer's brother or cousin. However, Homer is an only child (at least, Herb and Abbie are not seen regularly). It seems more likely that he is Marge's brother. She presently has only two sisters (Patty and Selma) and has only mentioned him once; but she was quite ashamed and said she would never speak of him again, which makes it more likely that he was her relative, not Homer's. Uncle Arthur is currently deceased. He used to have a saying, "Shoot 'em all and let God sort 'em out," until one day he put his theory into practice, and it took 75 federal marshalls to bring him down".[1] Another possibility is that Uncle Arthur was a great-uncle.

You may want to update the Wikipedia with your more complete info. Thanks.

Answer 1

"The Boy Who Knew Too Much"
Bart: Mom, what if there's a really bad crummy guy who's going to jail but i know he's innocent?
Marge: Well Bart, your Uncle Arthur used to have a saying "Shoot 'em all and let God sort them out." Unfortunately one day he put his theory into practice. It took seventy-five Federal Marshals to bring him down. Now let's never speak of this again.

Uncle Arthur is clearly Bart's uncle. Therefore, he would be either Marge or Homer's brother or cousin. However, Homer is an only child (at least, his half-siblings Herb and Abbie are not seen regularly). It seems more likely that he is Marge's brother. She presently has only two sisters (Patty and Selma) and has only mentioned him once; but she was quite ashamed and said she would never speak of him again, which makes it more likely that he was her relative, not Homer's. Clearly, Uncle Arthur is currently deceased. There is another possibility that Uncle Arthur was a great-uncle.