William Hall Macy, Jr. (born March 13, 1950) is an American actor. He is also a teacher and director in theater, film and television. His film career has been built mostly on his appearances in small, independent films, though he has appeared in summer action films as well. Macy has described his screen persona as "sort of a Middle American, WASPy, Lutheran kind of guy... Everyman".

Macy was born in Miami, Florida, and grew up in Georgia and Maryland. His father, William Hall Macy, Sr., was awarded the Distinguished Flying Cross and an Air Medal for flying a B-17 Flying Fortress bomber in World War II; he later ran a construction company in Atlanta and worked for Dun & Bradstreet before taking over a Cumberland, Maryland-based insurance agency when Macy was nine years old. His mother, Lois, was a war widow who met Macy's father after her first husband died in 1943; Macy has described her as a "Southern belle". Macy has a half-brother, Fred Merrill, from his mother's first marriage.

Macy describes himself as a "jokester", though he was relatively shy until high school. After his brother taught him to play guitar, he sang a song in a talent show, much to the crowd's approval. He later ran for class president, though he had a poor academic record. After graduating in 1968 from Allegany High School in Cumberland, Maryland, he participated in the anti-war hippie movement, and took copious amounts of drugs, including marijuana and LSD. Macy studied veterinary medicine at Bethany College of West Virginia. By his own admission, a "wretched student," he transferred to Goddard College and became involved in theatre where he performed in ensemble productions of Threepenny Opera, Midsummernight's Dream and a wide variety of contemporary and improvisational pieces. That is where he first met David Mamet. He moved to Chicago, Illinois, after graduating in 1971 and got a job as a bartender to pay the rent. Within a year he and David Mamet, among others, founded the successful St. Nicholas Theater Company, where Macy originated roles in a number of Mamet's plays, such as American Buffalo and The Water Engine.