He passed away in Livermore, California on Monday night (14Jan13). The cause of death remains unknown.
The actor is best known for playing businessman Phillip Drummond, the adopted father of Gary Coleman and Todd Bridges' young characters, on the hit U.S. TV sitcom.
Bain's daughter, Jennifer, tells TMZ.com, ""He was an amazing person. He was a lot like Mr. Drummond, but much more interesting in real life. He was an amazing father.""
The actor, who would have celebrated his 90th birthday on 4 February (13), was born in Alberta, Canada and went on to serve in the Canadian Army. Once his service was completed, he moved to New York, where he studied at the American Academy of Dramatic Arts and later became a U.S. citizen.
The actor then launched his career on Broadway, appearing in productions of The Iceman Cometh, An Enemy of the People and Uncle Vanya, before landing his big break on soap opera Dark Shadows.
In addition to his role on Diff'rent Strokes, he also starred in Maude and a handful of movies, such as Barbra Streisand's Up the Sandbox and Woody Allen's Bananas.
Bridges is leading the tributes to Bain, and a statement from the devastated star reads: ""I am deeply saddened by the sudden passing of Conrad as we were looking forward to celebrating his 90th birthday next month. In addition to being a positive and supportive father figure both on and off-screen, Conrad was well-loved and made going to work each day enjoyable for all of us. He will be missed, but never forgotten.""