Agnes Skinner is Principal Seymor Skinner's very controlling elderly mother.  Agnes was actually revealed to have adopted Seymour during "The Principal and the Pauper."  Agnes also often serves as a friend of Marge in many adventures.

Agnes Skinner Quotes

I was in love with a soldier boy on leave from Korea. It was a fifties style of romance, five minutes of sex and a lifetime of regret. He went back to his war and I went back to my dream of pole vaulting in the Helsinki Olympics. But there was a bump in the road, a bump named Seymore.

Agnes [in flashback]

Agnes: Where did you learn to sweep like that?
Marge: I've been training all my life. I once swept red wine off a white carpet.

The Simpsons Quotes

Repent! Repent! Before it's too late! (giggles) I always wanted to do that in a New England church.

Lisa

You know, you remind me of a poem I can't remember, and a song that may never have existed, and a place I'm not sure I've ever been to.

Grampa