Terrence Hardiman, best known for playing the title role in the CBBC series The Demon Headmaster, has died at the age of 86, his agent has said.
The stage and screen star also appeared in TV series such as The Crown, Wallander, Doctor Who and Prime Suspect.
"Goddammit, we've lost Terence Hardiman. I honestly can't think of anyone who could have played the Demon Headmaster better," one fan wrote on Twitter as the news broke this morning.
"To this day I struggle to think of a more terrifying figure from my childhood," another added, referring to Hardiman's iconic portrayal of The Demon Headmaster.
A third added: "Another childhood legend gone. This was amazing, and terrifying back in the day."
Born in 1937 in Forest Gate, Newham, London, Hardiman studied English at Fitzwilliam College, Cambridge, where the late actor got the acting bug.
Hardiman, who would go on to become an icon to a generation of kids, performed for The Marlowe Society and the Cambridge University Amateur Dramatic Club, alongside many of his future screen co-stars such as Derek Jacobi.
Throughout his illustrious, Hardiman appeared in a number of popular TV shows, including The Bill, Prime Suspect and Juliet Bravo, and often played figures of authority,
From Nazi-era personnel and police officers to doctors and barristers, Hardiman could always be counted on to deliver a powerful performance.
But it was his stint as an evil headmaster in the late 90s that brought the actor to the attention of young children - even managing to still scare a few three decades on.
Based on the children's books by Gillian Cross of the same name, The Demon Headmaster terrified a nation of youngsters when it premiered on CBBC in 1996, mainly thanks to Hardiman's portrayal of the evil teacher.
The Demon Headmaster hid his piercing green eyes behind dark glasses - only taking them to hypnotise his victims after telling them: "Look into my eyes".
The children's drama originally ran between 1996 and 1998 but Hardiman reprised his role in 2019, when a direct sequel of the original series began with with Nicholas Gleaves taking over as the titular character.
But despite playing a baddy on screen, Hardiman was thought to be a pleasure to deal with when the cameras stopped rolling.
"Awfully sad news about Terrence Hardiman, who has passed away aged 86. Terrified a generation as the Demon Headmaster, but could not have been more of a good-natured gentleman in real life," one fan wrote on Twitter following the actor's agent announcing his death.
Another mourning fan mused how the actor was so synonymous with one his famous roles that many didn't even know his real name.
"Sad news, as he was a big part of my childhood," they began as they shared the news of Hardiman's death on Twitter. "But also, I can't believe how this is the way 90% of people my age are finding out the name of the actor who played The Demon Headmaster."
Another tribute reads: "A brilliant actor, obviously great as The Demon Headmaster and also terrific in the final series of Secret Army.
"Allegedly he kept the Headmaster's glasses prop after filming, because he thought it would be a character people would want to see him return to."
Hardiman's prediciton came true, when he reprised his role for The Demon Headmaster sequel just a few years ago.
"I just make an appearance for a while, just a cameo," Hardiman told RadioTimes.com in 2019.
"So it’s not about me. It’s the new lot and that’s lovely. I’m not there for long. So I won’t frighten you for too long!"
He went on to confess he was slightly nervous to don the dark glasses once again, saying: "I thought, well, it’s 22 years since I played that part on television.
"Are people going to say, 'What the devil is he doing that for? Doesn’t anyone else want him to do anything else?'
"No, it wasn’t quite like that, but I was slightly nervous about meeting new people. I didn’t want them to start saying, 'Why have we got this old chap in again?'."
Towards the later years of his career, the late actor enjoyed a cameo on BBC soap Doctors and appeared as Hawthorne in the episode of Doctor Who, The Beast Below in 2010.
Hardiman is survived by his wife Rowena and his two children.
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