Abruptly departed: Valerie Harper, center
Played: Mother Valerie
Lasted: Two seasons (1986-1987)
Why she left: Harper disagreed with the producers' plans to introduce more slapstick humor and shift attention to the younger cast members. After being fired, Harper sued for breach of contract and won $1.4 million.
How it went down on air: Valerie dies in a car accident. Michael's sister Sandy moves in to help the family through their time of loss.