Michael Constantine (born Gus Efstratiou (or Ευστρατίου); May 22, 1927 – August 31, 2021) was a Greek-American actor. He is best known for his portrayal of Kostas "Gus" Portokalos, the stubborn Greek father of Toula Portokalos (Nia Vardalos), in the film My Big Fat Greek Wedding (2002). For his performance, Constantine won a Satellite Award for Best Supporting Actor – Musical or Comedy.

Early in his career, Constantine earned acclaim for his television work, especially as the long-suffering high school principal, Seymour Kaufman, on ABC's comedy-drama, Room 222, for which he won the Primetime Emmy Award for Outstanding Supporting Actor in a Comedy Series in 1970. He was again nominated by the Emmy Awards, as well as the Golden Globe Awards, the following year. After the conclusion of Room 222, Constantine portrayed night court magistrate Matthew J. Sirota on the 1976 sitcom Sirota's Court, receiving his second Golden Globe nomination. In his final acting performance, Constantine reprised his role as Gus Portokalos in My Big Fat Greek Wedding 2 (2016).

He played Joe Dix in the original series episode "Counterweight".