His agent Lynda Ronan said: "Sam Kelly died peacefully this morning after a long illness bravely fought. He does not leave any family but a host of friends who were his chosen family. His death is a great loss to them and the profession."
Born in Manchester, Kelly spent five years in regional rep and then a year with the Young Vic company under Frank Dunlop. Despite his association with TV work, he returned regularly to the stage throughout his career.
His most famous TV role, as Captain Hans Geering in ‘Allo, ‘Allo, even provided him with a crossover vehicle in a stage production that toured the UK and then transferred for a West End season.
His many other stage credits over the years, in the West End, at the National, Royal Court and elsewhere, included The Government Inspector, Run for Your Wife, Dead Funny, The Odd Couple, A Funny Thing Happened on the Way to the Forum, Much Ado About Nothing and Aladdin.
He withdrew from playing the Wizard in Wicked - a role he first played in 2009/10 - in January this year due to illness. He was replaced by Martyn Ellis.
Speaking to WhatsOnStage in 2005, Kelly said his interest in theatre was sparked as a young boy growing up in the North West: "When I saw The Wind in the Willows at the Liverpool Playhouse at the age of eight, I said to myself 'that's what I'm going to do'."
Tributes have poured in on Twitter.
Actor Mark Gatiss wrote: "Desperately sad news that the wonderful Sam Kelly has left us. Such a funny, talented man and one of the good guys. RIP Bunny Warren".
Playwright Mark Ravenhill said: "Sam Kelly was honestly one of the kindest most generous people I've worked with. And of course a great talent."
And Kelly's former Wicked co-star Sam Lupton tweeted: "Never known a man who brought so much happiness to people as Sam Kelly. I'm honoured to have known you! A man who is truly missed."
What are your fondest memories of Sam Kelly? Please share them in the comments below