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

Principal Skinner: (thinking) I know you can read my thoughts, Bart. Just a little reminder. If I find out you cut class, your ass is mine. Yes, you heard me. I think words I would never say.
Homer: (thinking) I know you can read my thoughts, boy. (singing) Meow meow meow meow, meow meow meow meow, meow meow meow meow meow meow meow meow.

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]

The Simpsons Quotes

Homer: (Wearing glasses) The sum of the square roots of any two sides of an isosceles triangle is equal to the square root of the remaining side!
Man: (From inside a bathroom stall.) That's a right triangle, you idiot!
Homer: D'oh!

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