Mother Penguin

A character type of stern, elderly nun, who acts as a Sadist Teacher at a Catholic school (possibly of the Boarding School of Horrors variety) but may (or may not) be looked back upon with some affection.

Not to be confused with Everything's Better With Penguins.

Comic Books

 * This trope played a part in the origin of Alpha Flight's Aurora / Jeanne-Marie Beaubier. The not-so-fond memories kind.

Film

 * The Trope Namer is from The Blues Brothers
 * The reverend mother for much of the first Sister Act movie.
 * Sister Aloysius in Doubt is basically an example of showing this character type as having Hidden Depths
 * Rosalind Russel's character in The Trouble With Angels was one of these character types.

Live Action Television

 * Sister Dominick from The Suite Life of Zack and Cody. Who knew that nuns could be so sarcastic?

Newspaper Comics

 * Ronald-Ann had one of these in her Catholic school in Berkeley Breathed's Outland.

Theater

 * Sister Mary Ignatius Explains It All For You by Christopher Durang. Just... that. The entire play is focused on this character type.
 * The popular "interactive play" Late Night Catechism is based upon this trope.

Western Animation

 * Bart's teacher is one of these when he goes to Catholic school in the episode "The Father, The Son, and the Holy Guest Star."