Loretta Long

Loretta Long plays Susan on Sesame Street.

She was one of the original cast members in 1969.

She received her Ph.D. in Urban Education in 1973 from the University of Massachusetts, while she was starring on Sesame Street.

Official bio
(from sesameworkshop.org):

Loretta Long (Susan) has been with Sesame Street since its first season. Before that, she appeared on the public television program Soul, and in summer stock productions of Guys and Dolls, Milk and Honey and Sweet Charity. She is a distinguished former schoolteacher with a doctoral degree from the University of Massachusetts. Dr. Long is a published author, visiting scholar and educational consultant. She plays Susan, Gordon's wife and Miles' mother. Over the years, her character has evolved from housewife to nurse to working mother.

Trivia

 * Loretta Long was also the voice of Roosevelt Franklin's Mother, and she also voiced an Anything Muppet mother in the song, "Five People in My Family", alongside Jim Henson, Frank Oz, Bob McGrath, and Carroll Spinney.