Doctor Who star Elisabeth Sladen, who was also in spin-off series The Sarah Jane Adventures, has died aged 63.
Sladen appeared as Doctor Who assistant Sarah Jane Smith in the BBC television sci-fi series between 1973 and 1976, opposite Jon Pertwee and Tom Baker.
The Liverpool-born actress appeared in four series from 2007 of The Sarah Jane Adventures on children's channel CBBC.
Sladen had been battling cancer for some time and leaves actor husband Brian Miller and daughter Sadie.
A BBC spokesman said: "It is with much sadness that we can announce Elisabeth Sladen, the much-loved actress best known for her role as Sarah Jane Smith in Doctor Who and CBBC's The Sarah Jane Adventures, passed away this morning."
Doctor Who star David Tennant told BBC Radio 1's Newsbeat that he had been "bewitched" by the actress's performances in the show when he was a boy.
He added that he would "never forget" working with her when Sarah Jane Smith returned to the show during his tenure as the 10th Doctor.
"Having been such a huge part of my childhood, she was everything you hoped she would be when you met her. She was extraordinary," he said.
John Barrowman, who co-starred with Sladen when she returned to Doctor Who in 2006, paid tribute to the star via micro-blogging site Twitter.
"I loved my time on the Tardis with her. I am proud to have worked with such an icon of the sci-fi world," he wrote.
"Your Doctor Who family are very sad and will miss you and your beautiful smile. She was a delight. Can't tell you how sad I am."
Russell T Davies, creator of The Sarah Jane Adventures, said: "I absolutely loved Lis. She was funny and cheeky and clever and just simply wonderful. The universe was lucky to have Sarah Jane Smith, the world was lucky to have Lis."
Doctor Who executive producer Steven Moffat said she had been a "ferociously talented actress".
'''Never meet your heroes,' wise people say. They weren't thinking of Lis Sladen," he added.
"Sarah Jane Smith was everybody's hero when I was younger, and as brave and funny and brilliant as people only ever are in stories.
"But many years later when I met the real Sarah Jane - Lis Sladen herself - she was exactly as any child ever have wanted her to be. Kind and gentle and clever and a ferociously talented actress, of course, but in that perfectly English unassuming way."
Sladen began her career as an assistant stage manager at the Liverpool playhouse.
Her first role on stage was playing a corpse, and she made her screen debut in the 1965 film Ferry Cross the Mersey as an extra.
Her first role leading role was Desdemona in Othello, before the actress landed the role of a barmaid in Coronation Street for six episodes.
She has also appeared in several other hit TV shows, including Z-Cars, Public Eye, Some Mothers Do 'Ave 'Em and Special Branch.
But it was her role in Doctor Who that gained her the most recognition.
Sladen first appeared as Sarah Jane alongside the third Doctor, Jon Pertwee, and stayed for three-and-a-half series, also working with Pertwee's successor, Tom Baker.
Her character, a journalist, was renowned for being inquisitive and stronger than some of the Doctor's other assistants.
After her time in the Tardis, Sladen returned to her native Liverpool where she worked in theatre.
She reprised her Doctor Who role on several occasions over the years and was given her own spin-off series on CBBC in 2007, in which she appeared with the most recent two Doctors, David Tennant and Matt Smith.
In 2006, ahead of rejoining Doctor Who, Sladen said of the show: "I think it has lovely layers and I'd defend the programme to anyone.
"I'm very emotionally part of that programme and I think a lot of the people who worked on it are. You used to love going to work every day."
CBBC controller Damian Kavanagh said he was "deeply saddened and shocked by the news of Lis's untimely death".
"Lis brought joy, excitement and a sense of wonder to her many fans in her role as Sarah Jane Smith. She was adored by our young audience and I know all of them will miss her as much as I will," he said.
Keith Jones, the director of BBC Wales, which makes The Sarah Jane Adventures, said: "The Sarah Jane Adventures has been one of the most successful children's programmes on television in recent years - and without Elisabeth Sladen it would not have happened.
"A brilliant presence on screen and on set, she brought the excitement and energy of the Doctor Who family of programmes, of which we are very proud at BBC Wales, to a whole new generation. She will be missed by all at BBC Wales who worked with her."
Sladen's agent Roger Carey described her as a "dear friend".
He said: "She was so positive about life and her natural energy was intoxicating. She couldn't believe her luck when her career was resurrected in her own series."
Doctor Who returns on Saturday and a spokeswoman for the show said that "something suitable is being planned" as a tribute to the late actress.