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

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!

Wow, now I see why they call you Miss Hoover. You must have been vacuuming for an hour.

Bart