The character actor played the role of 'The Ugly' while Eastwood and Lee Van Cleef were 'Good' and 'The Bad' in the 1966 Italian Spaghetti Western film, directed by Sergio Leone.
Wallach, who was born on December 7, 1915, to Polish immigrants, made his movie debut as a cotton-gin owner trying to seduce a virgin in Elia Kazan's 'Baby Doll' in 1956.
The prolific actor died on Tuesday, his daughter Katherine told The New York Times.
He was given an an Honorary Academy Award at the second annual Governors Awards in 2010 for his contribution to cinema.
Wallach is survived by his actress-wife Anne Jackson, who he was married to for 66 years and children.
His other famous role is in John Sturges' 1960 film 'The Magnificent Seven', which was a remake of Akira Kurosawa's 1954 Japanese classic 'Seven Samurai' where he played the antagonist.
Wallach was also memorable as a hitman looking to retrieve heroin stuffed in a Japanese doll in Don Siegel's 'The Lineup', as Guido in John Huston's 'The Misfits' opposite Clark Gable and Marilyn Monroe, as Audrey Hepburn's suitor in 'How to Steal a Million' and as a mafioso in 'The Godfather: Part III' (1990).
The actor appeared in more than 90 films, including Oliver Stone's 'Wall Street: Money Never Sleeps' and Roman Polanski's 'The Ghost Writer'.
He had an equally successful stint on television, winning an Emmy for his role in ABC's 'Poppies Are Also Flowers'. He also earned popularity on 'Nurse Jackie' and Mr Freeze on TV's Batman.