He's famous for his exposés of the seedy side of LA life, interviewing everyone from porn stars to pet obsessives in a bid to shine a light on the parts of Hollywood where the cameras don't go.
Now Louis Theroux has turned his attentions to a completely different part of LA life - the dying - and unearthed an incredible survival story in the process.
When Theroux first met Langston, 22, he was in a coma and not expected to survive. But 37 days later and in the face of overwhelming odds of a million to one, the college athlete woke up.
New direction: Theroux goes behind the scenes at LA's Cedars-Sinai to explore the dying process
'I was amazed,' reveals Theroux. 'The doctors had repeatedly told us – and told his family – that the best-case scenario for him would be that he remained in a vegetative state. Best case!
'So to have him wake up and walk again and converse normally was mind-blowing. I remember being in the office when my director came off the phone from Langston’s sister and said he’d woken up. I didn’t believe him.
'It just goes to show, doctors don’t know everything. Seeing him reunited with his twin brother after he woke up was one of the most moving things I’ve ever seen.'
So how did a 22-year-old athlete come to be in a coma? The answer is a drug overdose that left him with severely compromised liver and kidney function and traumatic brain damage.
Doctors at LA's Cedars-Sinai Medical Center were convinced that the damage was too severe to make recovery possible and had told the family that it would be better to let him go.
Harrowing: Langston in hospital with his Aunt Sheila and Louis. Doctors were convinced he wouldn't survive
Survivor: Incredibly, and against all odds, Langston woke up after 37 days in a coma
The family, by contrast, were equally convinced that he would survive and their faith was rewarded when after more than a month, he opened his eyes.
'I'm grateful and I'm thankful to God,' his delighted sister Andrea tells Theroux, 'but I knew he was going to get better - I knew he was going to be OK.'
That optimism is at the heart of Theroux's new film, LA Stories: Edge of Life; an optimism that sees doctors, families and patients continuing to treat patients long after they would have been dispatched to a hospice in the UK.
'It’s the nature of the way healthcare is funded in America,' explains Theroux. 'If you have insurance, then beyond a certain threshold of cost, everything is covered, with virtually no upper limit.
'So there is a temptation to try everything. Which in some ways is good because there are so many options available.
'But it’s also the case that, given the vast amounts the US spends on healthcare (compared with other industrialised nations), the US life expectancy is not what it should be.'
And while Langston manages a miraculous recovery, the other severely ill stars of the show; Donta, a 31-year-old with rectal cancer and Javier, a 29-year-old suffering from leukaemia; do not.
'I knew they were at a high risk of dying soon,' explains Theroux. 'It was deeply affecting to see them live through some of the most dramatic and upsetting experiences of their lives.
'But, as strange as it may sound, both Donta and Javier took strength from having the camera there as a witness to their struggle.
Miracle: Langston with his mother Lyle and sister Ashley - neither of whom ever gave up hope
'I'm good': What Langston, pictured with twin brother Lorne, when he returned to thank them
'Donta had always worked on the fringes of show business and he loved the idea of being on a mainstream TV programme. He wrote glowingly about it on Facebook.
'And Javier seemed to appreciate having someone from "the outside" talking to him about what he was going through.'
The tale of the two men also illustrates the differences between end-of-life care in the US and the UK; not least in terms of the amount of money involved.
In Donta's case, the treatment he received in hospital cost more than $2 million - a lot, you might imagine, for what ultimately turned out to be a futile attempt to save him.
So is it right to spend so much on one man that could have been put to use elsewhere? Theroux finds the question a tough one to answer.
'He had a massive amount of surgery to remove his anal cancer – which had spread to his liver,' he muses.
'This was a long-shot procedure, especially given that he had a weakened immune system. His recovery was slow and painful, and in fact his wound never healed, which contributed to his death.
Not so lucky: Javier, who also appears in Theroux' film, in happier times before succumbing to leukaemia
Last moments: Javier married his girlfriend a few days before he died; a moment captured in the documentary
'It seems to me that – in a world of finite resources – it wasn’t the best use of the two million. But I try to put myself in Donta’s position and I can understand the motivation to get it done, and likewise the doctor’s urge to do the best for Donta.'
Questions about morality and money aside, at heart, the film is about death and how people deal with it - whether that's staving it off for as long as they can or accepting it.
Parts are quite simply heart-breaking: The moment when Donta sobs after being told that nothing more can be done for him or when Javier marries his girlfriend in a bedside ceremony.
Ultimately, it's oddly uplifting both because of Donta and Javier's bravery and because of Langston's dramatic recovery.
After 37 days in intensive care and seven weeks in rehab, the man who everyone thought would end his life as a vegetable strides, beaming, back into the hospital to thank the staff who saved his life.
'I'm good,' he tells the doctor. Proof that, for all its perceived flaws, the American health system can provide some lucky families with miracle.
Louis Theroux's LA Stories: Edge Of Life, Sunday night at 9pm on BBC2
LOUIS THEROUX' LA LIFE: THE FILM-MAKER EXPLAINS WHY HE CONTINUES TO BE FASCINATED BY THE CITY OF ANGELS
He's no stranger to the weird and wonderful and now Louis Theroux is to tackle one of the weirdest and most wonderful religions of them all - Scientology.
'Scientology is the quintessential Hollywood religion,' he explains. 'I’ve been trying to make [the film] for years and now we’ve got funding to do it as a feature documentary film.
'I just put out an appeal on Twitter for Scientologists to speak to me for the film. They tend not to do much media so we’ll have to wait and see what comes back.'
But that's not all. Now based in Los Angeles, a city that he continues to find fascinating, Theroux is planning more films, although he says subjects are still to be finalised.
'LA embodies the best and worst of America,' he explains. 'Divisions of wealth, vulgarity, energy, breathtaking landscapes, beaches, mountains, deserts, and tracts of crappy housing covering much of the above.
'Talented, funny, creative people creating art that entertains the world and also a certain level of incuriousness about that world.
'People run the gamut. There is a prejudice that Angelenos are shallow and touchy-feely. That is definitely one part of the truth.
'There is a surface friendliness that doesn’t always run that deep, but then surface friendliness is better than surface unfriendliness.'
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