TORONTO - Allan King, the acclaimed Canadian documentarian who took viewers on a harrowing journey into a home for troubled children in "Warrendale" and trained his unflinching lens on a crumbling marriage in "A Married Couple," has died at age 79.

His family announced the death through a news release. King had been diagnosed with a brain tumour in April.

"A giant of Canadian cinema has departed the scene," Piers Handling, director of the Toronto International Film Festival, said Monday."Unquestionably, one of the most influential filmmakers to have ever stepped behind a camera in the country, actually. Allan's impact on the documentary is right up there among some of the major international documentary filmmakers in the world."

Born in Vancouver, King began his career at the CBC in the 1950s and then moved on to the BBC.

In 1967, he shocked the cinematic world with "Warrendale," which looked at the lives of children at a Toronto facility of the same name. The film was commissioned by the CBC but the public broadcaster initially refused to air it because the children in the film could be heard swearing.

It was eventually released theatrically to huge acclaim and has become requisite viewing in film schools.

"Obviously for someone like me in my generation as a documentary filmmaker, he's a giant," said filmmaker Jennifer Baichwal ("Manufactured Landscapes," "Act of God").

"His reputation and his work, those things are huge."

King was at the forefront of the 1960s movement called cinema verite -- or "cinema of truth" -- a realistic style of filmmaking that shied away from interviews, music, narration or sound effects. His contemporaries included D.A. Pennebaker and Fred Wiseman.

King referred to his technique as "actuality drama," and immersed himself in the lives of his subjects, spending days with them to gain their trust.

In his 1969 film, "A Married Couple," King turned his lens on advertising copywriter Billy Edwards and his wife Antoinette -- a Toronto couple struggling to keep their union intact.

At times difficult to watch, the film was another groundbreaker, as it invited viewers inside the couple's home to witness their everyday fights and struggles.

New York Times critic Clive Barnes called "A Married Couple" "quite simply one of the best films I have ever seen."

"Just living with those people, gaining their trust, observing them, getting them completely natural on camera to the point where they just were not even aware that the camera was around (was innovative)," notes Handling.

"(King) took hours and hours -- 90, 100 hours -- of footage ... trimmed it down to an hour and a half. And that was revolutionary documentary filmmaking. That kind of ratio of shooting was unheard of. Documentaries were largely very structured, almost dramatically written, with heavy voiceover."

Baichwal says King's dedication was balanced by a deep sensitivity to his troubled subjects, allowing the viewer unusual access without appearing exploitive.

"He managed to ... convey what was happening in front of the camera in a completely honest way and yet the ethics of the way he did it were so strong that the two things came together in a way that I think is hard to achieve in documentary film," she said.

"And you were always aware of how important his ethics were and also how pristine they were in that context of where he was going in his film. And at the same time you got the feeling of this incredible intimacy of what was happening in front of the camera."

While he continued to work on documentaries, King also tried his hand at feature film. His first effort, "Who Has Seen The Wind," was released in 1976 and won the Golden Reel Award for the highest grossing Canadian film of the year.

During the late 1980s and '90s, King worked in TV, directing many episodes of "Road to Avonlea." His accolades include a Gemini Award for best direction in 1992, a lifetime achievement from the Directors Guild of Canada and his appointment as an Officer of the Order of Canada in 2006.

King's other documentaries include 1973's "Come on Children," in which several young Toronto residents were put on a farm to see how they would fare without adults and the 1983 unemployment doc "Who's in Charge?"

Retrospectives of his work have been held in cities around the world, including Toronto, London, Rome, Prague and at the Museum of Modern Art in New York.

"We have lost one of the greats who up to the last never ceased being inventive, wondering at and questioning the world about him," said Tom Perlmutter, chair of the National Film Board. "It is a great loss."

He leaves behind his wife, Colleen Murphy, and four children.