Diane is Pete's first wife, an intense overachiever, and the mother of teenagers Hillary and Warren. Diane is incredibly accomplished: she's a world-renowned orthopedic surgeon and won the silver medal in the 1988 Olympics for the 100-meter breaststroke. In her spare time she enjoys going to museums and correcting the tour guides.
Not surprisingly, Diane and her strong personality intimidate Pete, Jackie, and Kate. Being so successful, Diane can be impatient and critical of those who cannot match her level. She believes the parents are only as strong as the weakest link and doesn't want Kate undoing all the wonderful parenting Diane believes she has done.
Under her impenetrable exterior, Diane does have a warm heart and vulnerabilities. She goes over the kids' homework with them in painstaking detail because she cares about their futures, and she snoops through their rooms because she doesn't want them getting into trouble. She loves her children dearly, just expresses it differently than the other parents.