Actress Helen McCrory, known for her roles in Peaky Blinders and three Harry Potter films, has died of cancer at the age of 52, her husband, the actor Damian Lewis, announced.
He said he was "heartbroken", and that she was a "beautiful and mighty woman".
He wrote: "She blazed so brightly. Go now, Little One, into the air, and thank you."
Harry Potter author JK Rowling led the tributes, writing that it was "simply heartbreaking news".
McCrory was also known for her long and acclaimed career on stage, and the National Theatre's artistic director Rufus Norris said she was "unquestionably one of the great actors of her generation".
Peaky Blinders creator Steven Knight said: "Helen was one of the great actors of her generation. She was so powerful and controlled and this is so sad."
Cillian Murphy, who played Tommy Shelby in the show, added he was "broken-hearted to lose such a dear friend", describing her as "a beautiful, caring, funny, compassionate human being".
"She was also a gifted actor - fearless and magnificent. She elevated and made humane every scene, every character she played," he said, adding it was "a privilege to have worked with this brilliant woman... I will dearly miss my pal".
BBC director of drama Piers Wenger added: "Helen was one of the finest actresses this country will ever see."
Homeland star Lewis said she had died "after an heroic battle with cancer".
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"The beautiful and mighty woman that is Helen McCrory has died peacefully at home, surrounded by a wave of love from family and friends," he said.
"She died as she lived. Fearlessly. God we love her and we know how lucky we are to have had her in our lives."
McCrory married Homeland star Lewis in 2007 and they had two children. Last year, the couple raised more than £1m to provide NHS workers with meals from high street restaurants during the pressures of the coronavirus pandemic.
Comedian Matt Lucas, who worked with them on the FeedNHS campaign, tweeted that she "will be remembered not just for her remarkable stage and screen performances, but also for her selflessness and generosity".
In April 2020, McCrory and Lewis appeared on the BBC's Newscast and she explained why they set up FeedNHS.
"We've got lots of friends in the NHS and when this outbreak happened, they said one of the big problems they had was all the cafes and restaurants around the hospitals were closing. And the hours they were doing were longer and longer, and they weren't able to get food.
"We decided we wanted to try and get food to these people working such long hours and weren't able to."
The couple also appeared just weeks ago on Good Morning Britain, to talk about charity work for the Prince's Trust.
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In her tribute, Rowling wrote: "I'm devastated to learn of the death of Helen McCrory, an extraordinary actress and a wonderful woman who's left us far too soon.
"My deepest condolences to her family, especially her husband and children."
McCrory played Narcissa Malfoy, the wife of Lucius Malfoy and Draco's mother, in Harry Potter and the Half-Blood Prince and Harry Potter and the Deathly Hallows: Part 1 and Part 2.
The actress was perhaps best known for playing Aunt Polly, the matriarch of the Shelby clan, in all five series of hit BBC period gang drama Peaky Blinders from its start in 2013.
"She really is the brains with Tommy behind the family, and you see the difference of how to rule," she said when speaking about 2014's second series.
In his tribute, the BBC's Piers Wenger said: "Helen's fearlessness made every part she played unique and unmissable.
"Her body of work speaks of her extraordinary talent, what it doesn't speak of is her kindness, intelligence and sense of fun. This is too soon, too cruel."
Her other screen roles included the MP Clair Dowar in 2012 James Bond movie Skyfall, and former Prime Minister Tony Blair's wife Cherie in the films The Queen and The Special Relationship.
She provided the voice of Stelmaria, Lord Asriel's snow leopard daemon, in the recent BBC One TV series His Dark Materials, and the show's Twitter account called her "uniquely talented".
Bafta, the British film and TV academy, wrote: "We're sad to hear of the death of actor Helen McCrory. As well as fearless Polly Gray in Bafta-winning Peaky Blinders, she was in 2007 Best Film Bafta winner The Queen, amongst many other films and TV shows."
BBC One series Doctor Who also paid tribute to the actress, who appeared in 2010 episode The Vampires of Venice.
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As well as her film and TV credits, she played seven lead roles at the National Theatre, whose boss Rufus Norris said: "With her incisive wit and ferocious intelligence, she was one of the most charismatic and distinctive performers.
"She was also a deeply beloved member of this theatre's broader community."
She also worked at the Royal Shakespeare Company, the Almeida and the Donmar Warehouse, and earned rave reviews for her role in Uncle Vanya in London and New York in 2002 and 2003.
McCrory was nominated for two of London's Olivier Awards for playing Rosalind in As You Like It in 2006, and for The Last of the Haussmans in 2013.
'One of the greatest actors of our time'
Film and theatre director Sir Sam Mendes, who directed Skyfall, remembered her as "an astonishing talent, a fabulous person, and an absolute true original".
He said: "The film and theatre world has lost a one of a kind actress, and her family and friends have been robbed of an extraordinary, indomitable spirit. The world will be an infinitely poorer place without Helen in it."
McCrory also formed the theatrical production company The Public with fellow actor and Staged star Michael Sheen. On Friday, he said she was "so funny, so passionate, so smart and one of the greatest actors of our time".
He wrote: "From the first moment I met her when we were just kids it was obvious she was very special. It was an honour to work with her and know her. Much love to Damian and her family. Heartbreaking."
A diplomat's daughter, her family moved to Cameroon and Tanzania as a toddler, the latter of which she later described as "my most formative country".
"I loved Africa and it stays with you," she told BBC Radio 4's Desert Island Discs last year.
She said she caught the performance bug while performing in the school choir.
"That night I will never forget walking in and standing on that stage, having been not that interested up till then… Suddenly the orchestra started up and I sang so loudly, and the whole body vibrated," she recalled.
"It was the most extraordinary thing I'd ever been part of. It was a piece of music I would never ever be capable of writing, and I realised from a very young age I would never be original. I would never be a great artist.
"But what I could do is I could be part of another great artist's work. I could be an interpreter. That felt so good, not being me."
She spoke on Newscast about the coronavirus pandemic, saying it had been "so overwhelming".
"It seems fantastical, you think you're absolutely fine, you're pottering along, you're coping with it, cleaning, cooking, cleaning, cooking and you suddenly burst into tears, and it's the fear and it's the vulnerability coming out. And then you pick yourself up and you go along again, as if nothing happened, and it's surreal."
She added that during lockdown they had done "quite a lot of painting and music", and joked: "If you're still for too long, I will bleach you."
In 2003, she met Lewis when they both starred in a play called Five Gold Rings at the Almeida Theatre London.
"He makes me laugh, and that was quite apparent quite early on," she said. "He just never lets me get away with anything, and that would make me laugh even more. So I think we hit it off pretty quickly.
"We had a bumpy courtship… We are completely different as people, but we're very similar in our values and very rarely disagree about fundamental things."