Despite the fact that he had moved away from Canada, the CBC was the best client for his documentaries, which displayed a number of innovative techniques: mobility because they used lightweight cameras; grittiness from shooting on location and spontaneity from recording events as they happened rather than staging scenes according to a written script.
His first major feature documentary work was Warrendale , a film commissioned by the CBC about emotionally disturbed children at a mental health facility in Toronto. The late filmmaker Jean Renoir is said to have considered Warrendale the most remarkable documentary he had ever seen.
The film began as a commission in 1965 from Patrick Watson, the co-host and co-producer of the controversial This Hour Has Seven Days . Mr. Watson wanted Mr. King to profile John Brown, a Toronto child psychologist, who had pioneered a treatment for severely disturbed children by placing them in a surrogate family environment and "holding" them in a firm, but supposedly loving embrace when they acted out.
Mr. King spent a month getting acquainted with the children in one of the residential houses before bringing in his crew and equipment. Filming began two weeks later and lasted for five weeks. By then the children and the staff were so familiar with the camera crews and their omnipresent equipment that, for the most part, everybody forgot they were being filmed and began treating the cameras like another piece of furniture.
The effect was to give viewers an astonishingly intimate look inside the daily, horrific reality of these children and adolescents. Indeed, Warrendale was so disturbing and the language so outrageous - for the times - that the CBC, which had cancelled This Hour Has Seven Days in May, 1966, refused to broadcast the documentary.
Instead, Mr. King negotiated the rights to distribute Warrendale in cinemas. After an initial 13 week run in Toronto, it was subsequently screened around the world to stellar reviews, earning a raft of awards, including the International Critics Prize at Cannes and sharing the best foreign film at the British Academy of Film Awards with Michelangelo Antonioni's Blowup .
From troubled children, Mr. King turned his lens to unhappy adults by making a powerful and painful film about the disintegration of a relationship. A Married Couple is based on the lives of advertising executive Billy Edwards and his wife Antoinette, people Mr. King knew in Ibiza.
Again the crew shot many hours of footage and interviews, disarming the subjects until they spoke frankly about the fault lines and pressure points in their marriage. Clive Barnes, then film critic for The New York Times described it as "quite simply one of the best films I have ever seen." A Married Couple was featured at the Director's Fortnight at Cannes in 1970.
His third major chunk of emotional life was about disaffected teenagers. Entitled Come on Children , this 1973 documentary follows 10 troubled teenagers, including Alex Lifeson, who would later become famous as a guitarist with Rush, as they ramble about on a farm talking about life, existence and what's wrong with the world.
Mr. King followed the same techniques and instincts as he had in his two earlier documentaries, but the results were less successful. The problem was largely that kids sitting around talking, which is what teenagers do much of the time, is interesting mainly to themselves. Their lassitude and their ennui is boring to watch, no matter how essential a life process it seems to be.
In the early 1970s, after two lavishly praised but unprofitable documentaries and one that had earned neither kudos nor sales, Mr. King was close to bankruptcy. So, he turned away from documentaries and began making feature films.