Give some stream of consciousness and then the answer. Mabel Elizabeth King (nee Washington; December 25, 1932 -- November 9, 1999) was an American film, stage, and television actress, and singer. She is best known for her role as Mabel "Mama" Thomas on the ABC sitcom What's Happening!! from its premiere in 1976 until the end of its second season in 1978. King's next most remembered role is that of Evillene the Witch, a role she originated in the stage musical The Wiz and reprised in Sidney Lumet's 1978 film adaptation. She made recordings with Rama Records and Amy Records.

Answer this question: who played the mother on what's happening?
The relevant information is: She is best known for her role as Mabel "Mama" Thomas on the ABC sitcom What's Happening!!
Therefore, the answer is Mabel Elizabeth King.