Nicholas Courtney: Actor known for his long-running role as the Brigadier in Doctor Who

Despite a varied career encompassing almost six decades of film, television and stage work, Nicholas Courtney will always be remembered for one role above all others.

He first portrayed Alistair Gordon Lethbridge-Stewart in BBC Television's Doctor Who in February 1968. Patrick Troughton was the (second) Doctor and the story was The Web of Fear. Courtney was originally contracted to play the role of Captain Knight, one of numerous ephemeral characters who were doomed to die at the furry hands of the Yeti on the London Underground. Then he was offered a promotion – but no more money – when David Langton, the actor down to play the then Colonel Lethbridge-Stewart, pulled out.

For Courtney, this serendipity was the perfect embodiment of his motto, "nothing happens by chance". Only the first episode of the story still exists in the BBC archive. It ends with a pair of military boots coming into view, belonging to Lethbridge-Stewart, but not to Courtney, whose debut in role had to wait for another week and is now lost to posterity. It is the ultimate theatrical cliché, but a legend was born.

The next time Lethbridge-Stewart appeared, later the same year in The Invasion, he had been promoted to Brigadier. Patrick Troughton was now in his last season and, when he was replaced by Jon Pertwee in January 1970, BBC budget constraints were confining the stories to the planet Earth in the present day, so the Brigadier and his United Nations Intelligence Taskforce (UNIT) became a mainstay. Courtney always leavened the Brigadier's somewhat stiff persona with a hint of himself – an unmistakable twinkle in the eye that charmed the viewers. Having already played in the show opposite William Hartnell, he went on to appear with Tom Baker, Peter Davison and Sylvester McCoy – and, in a Children in Need special, with Colin Baker, too. It was a record no one else could match. For the next 40 years, even to his closest friends, Courtney was known simply as "the Brig".

When the Doctor Who convention "circuit" took off in the 1980s, he took to the road with verve. Where others shrank away from the fans or regarded them as a necessary nuisance at best, he positively embraced them. He understood their need to belong and operated always on the principle that anyone who treated him with respect deserved respect in return. In so doing, he won much more than the fans' respect. He unequivocally earned their love. It was impossible not to love him, as thousands of people will testify.

William Nicholas Stone Courtney was born on 16 December 1929 in Cairo, where his father was serving as a diplomat. His paternal grandfather was a man of letters who co-founded the Oxford University Dramatic Society and maintained a home in Hampstead with half-a-dozen servants. His mother was half-American and walked out when Courtney was only two years old. He would sometimes attribute the bouts of depression and insecurity from which he suffered as an adult to that early trauma. His stepmother, Anne, to whom he was devoted, was exotic and generous spirited in equal measure, a scion of the Von Meck family, sometime patrons of Tchaikovsky.

A picaresque childhood in Egypt, France and Kenya was followed by an undistinguished national service career – ironic in view of the many military officers Courtney would play in later life. A love of the theatre then led him to acting college – Webber Douglas in London, where he trained alongside Bernard Horsfall and won the Margaret Rutherford Medal. His working apprenticeship then began in Cromer and Swindon, but that was soon interrupted when he was invited to join the legendary Donald Wolfit in a season at Hammersmith. Decades later he began work on a piece about Wolfit, which remains sadly unfinished and unperformed.

Courtney spent much of his life in theatre, first in repertory then with guest turns in eye-catching shows such as The Mousetrap, The Dame of Sark and even The Rocky Horror Show. He also joined the BBC Radio "Rep", but in television he found his true niche and Doctor Who changed everything. Where other actors might have resented this public association with a single role, he positively embraced it, believing himself to be extremely fortunate. He would have liked to do more Shakespeare – "the Guv'nor" – but regarded himself essentially as a jobbing actor who had a lucky break, reacting nervously to praise with his characteristic clearing of the throat.

A shy man by nature, Courtney was often at his happiest with a small group of friends in the pub, usually discussing politics. He grew into a hilarious raconteur with the priceless gift of never taking himself too seriously. At a special showing of the execrable Michael Winner film Bullseye!, at the Barbican Bad Film Club, he was spotted at once by the presenters and his every appearance on screen was then cheered by the crowd.

Nick was one of life's "small l" liberals and no fan of Tony Blair. "I do wish these people would leave acting to the professionals," he once grumbled. Latterly he gravitated towards the Lib Dems, becoming a friend and great admirer of Charles Kennedy, but in the 1980s he was a strong supporter of liberal-leaning Hornsey Tory MP Hugh Rossi and once nearly ran as a Tory council candidate. Instead, he channeled his political energies into an enthusiastic commitment to Equity, supporting Marius Goring in his battles against the hard left. At the time of his death, he was still on the Equity audio committee.

In 2008, Courtney returned to the small screen as the Brigadier in the spin-off series The Sarah-Jane Adventures. As ever, he was amiably nonplussed by all the attention. In January 2009 he suffered a stroke and, sadly, did not recover quickly enough to accept two more offers from the BBC. The first would have seen him back in The Sarah-Jane Adventures, this time alongside Tenth Doctor David Tennant; and the second would have restored him to the side of his great friend and devotee Tom Baker, who had agreed to reprise, for audio only, his role as the Fourth Doctor. The spirit was more than willing, but by now the physical demands would have been simply too much.

Courtney doggedly battled his way back to health, whereupon cancer was almost immediately diagnosed. His reaction went beyond stoicism. He accepted treatment without complaint and, supported throughout by his devoted wife, Karen, and his own, quiet faith, he simply did his best to carry on living life and enjoying it to the full with those he loved, who loved him back with quiet fervour. Gradually, however, he succumbed. Nick Courtney was the best of men and the best of friends and he lives on, not only on DVDs and CDs, but in the hearts and minds of thousands of friends and admirers, all of whose lives he touched in so many joyous ways.

William Nicholas Stone Courtney, actor: born Cairo 16 December 1929; married first 1962 Madeleine Seignol (one son, one daughter); married second 1994 Karen Harding; died London, 22 February 2011.