William LeMassena (May 23, 1916 – January 19, 1993) was an American actor. He was best known for his roles in Broadway and off-Broadway productions, the film All That Jazz (1979), and the soap opera As the World Turns (1985–1992). LeMassena was born in Glen Ridge, New Jersey on May 23, 1916, the son of Margery L. (1883–1942) and William Henry LeMassena (1874–1944). He graduated from New York University.

LeMassena made his acting debut in the 1940 Broadway production of The Taming of the Shrew, starring Alfred Lunt and Lynn Fontanne. He then became a regular part of the Lunt's unofficial rep company of actors, including Sydney Greenstreet, Thomas Gomez, and Montgomery Clift, with whom he appeared in There Shall Be No Night and Mexican Mural.

LeMassena was a close friend of Montgomery Clift, with whom he was in a relationship for three years during the early 1940s. Although Clift publicly dated Phyllis Thaxter, he and LeMassena continued to see each other privately during the run of There Shall Be No Night. The relationship ended when LeMassena left to serve overseas. LeMassena said of his relationship with Clift, "…over the course of three years we bared our souls, and found out everything about each other." "Our affair was for me the most beautiful experience in my life.

He died of lung cancer at his home in New Suffolk, New York on January 19, 1993, at age 76.