Theodore William Lange III (/lændʒ/; born January 5, 1948) is an American actor, director and screenwriter best known for his roles as bartender Isaac Washington in the TV series The Love Boat (1977–1986) and Junior in That's My Mama (1974–75).

At City College, Lange was particularly active on the theatre scene and named Best Actor by the Black Students Association.

[3] After college, Lange started in theatre appearing in local Oakland productions and as guest artist in residence at the University of Santa Clara.

[6][7] After appearing in the film Black Belt Jones in 1974, he portrayed Junior on the series That's My Mama before landing the role of the ship's bartender, Isaac, on The Love Boat in 1977, opposite Gavin MacLeod.

In the early 1980s, following a letter of recommendation from Lynn Redgrave (whom he met on an episode of The Love Boat), Lange attended a summer school at the Royal Academy of Dramatic Art to perfect his Shakespeare acting skills.

He has penned 17 plays, including George Washington's Boy, a historical drama about the relationship between the first president and his favorite slave, along with the comedy Lemon Meringue Facade.

[5][9] Lange remained close to Gavin MacLeod, his acting mentor, who was a Palm Springs resident and saw his plays.

"[11] Before the American edition of FHM folded in 2006, Lange wrote a sex and advice column, titled "Ask Isaac", with adult film actress Jenna Jameson.