Roy Hart (born Rubin Hartstein; 30 October 1926 – 18 May 1975) was a South African actor and vocalist noted for his highly flexible voice and extensive vocal range that resulted from training in the extended vocal technique developed and taught by the German singing teacher Alfred Wolfsohn at the Alfred Wolfsohn Voice Research Centre in London between 1943 and 1962.
Roy Hart began learning Wolfsohn’sextended vocal technique at the Voice Research Centre in 1947 where many of his fellow students acquired unusual vocal flexibility and expressiveness, some of them developing voices with a range in excess of five octaves. 
In 1959 Roy Hart, having been a long-standing attendant of the Alfred Wolfsohn Voice Research Centre, began teaching acting classes to actors and drama students at various venues across London.
Following the death of Alfred Wolfsohn in 1962, Roy Hart formed a performing arts group comprising some who had studied at the Alfred Wolfsohn Voice Research Centre and others who had attended Hart’s acting classes. This company was called first the Roy Hart Actor Singers, and then the Roy Hart Theatre.
Under the direction of Roy Hart, the Roy Hart Theatre evolved into a group of performers who devised and presented experimental performances noted for the way the members utilized extended vocal technique to create verbal and nonverbaldrama and music, which had a substantial influence on the work of notable contemporaries of the European avant garde, including Peter Brook who subsequently incorporated extended vocal technique into his productions, Jerzy Grotowski, who made vocal expression a central feature to his rehearsal techniques and performances, Karlheinz Stockhausen who adapted works for Hart, and Peter Maxwell Davies who composed Eight Songs for a Mad King especially for Roy Hart’s voice.
Roy Hart died in 1974, shortly after the Roy Hart Theatre moved permanently from London to Malérargues, Southern France. However, the remaining members continued the work begun by Alfred Wolfsohn and extended by Hart, through teaching extended vocal technique and staging dramatic and musical performances that utilized a vocal range and flexibility greater than that commonly heard in speech and song. The Centre International Artistique Roy Hart (CAIRH) in Malérargues is still active today.