Milhouse is Barts geeky best friend and sidekick from school.
While well into his 40's, Principle Skinner still lives with his mother, an over bearing and evil woman. She makes his life a living hell, but he is compelled to care for her.

Skinner also has a checkered past, including time in Vietnam. His flashbacks and nightmares sometimes show the 'real' Skinner.

 Spent time in the Vietnam war
 Having a secret affair with Edna
 Real name is Armin Tanzarian
 Also known as "Spanky"

 Malibu Stacey
 Cover-Ups 
 Dog named Hercules
 Mr Burns