Like him, she was generously endowed with charm and intelligence, but her early years were dogged by shyness and lack of confidence. The story of their meeting in Edinburgh in 1926 became the stuff of showbusiness legend. He was a speech and drama teacher aged 28, she a shy 12-year-old. They were cast together in an amateur play being entered for a competition.
Naomi Plaskitt was smitten from the start. She later recalled, "In my world, adults often smiled, sometimes laughed, but never clowned. I must have been the best audience he ever had." Sim somehow persuaded Naomi's mother to take her out of school at 14 to become his secretary. Four years later they married:
I don't think it occurred to either of us that our relationship might appear unusual. We were together because we were always going to be together, the tall man looking older than his years and the small, shy girl looking younger than hers.
He talked her into auditioning for Rada but after two years she gave up any thoughts of becoming an actress. "Nobody told me to give up. Alastair was always the most important thing in my life and I wanted to make damn sure he was happy." They did, however, appear in one film together, Wedding Group (1936), in which Naomi played a maid in a Scottish manse, presided over by Sim's minister.
Soon after the outbreak of the Second World War, Sim appeared in a spy thriller in the West End called Cottage to Let (1941), in which a 15-year- old Cockney kid unmasked the villain. The kid was George Cole who went to spend the weekend with the Sims at their new home in the country and stayed on and off for the next 12 years. They gave the young Cole elocution lessons which later enabled him to play a wide range of social types, from middle-class George Bliss in the long-running radio series A Life Of Bliss to south London conman Arthur Daley in ITV's Minder.
Cole wasn't the only youngster to benefit from the Sims's generosity and love of youthful spirits. At least half a dozen others - "our boys" as Naomi called them - mostly unhappy at home, have cherished memories of life at Forrigan, the welcoming woodland retreat built by the couple near Henley-on-Thames in 1947. They also found time to have a child of their own, Merlith, who now lives at Forrigan with her own family and next door to George Cole, who remained close to Naomi Sim to the end.
Throughout Alastair Sim's career Naomi spurred him on and became his "personal director", as he dubbed her. Sim appeared in a number of plays by the Scottish writer James Bridie, who became a close friend. Bridie was grateful for Naomi's comments during rehearsals.
Sim's performances in films such as The Happiest Days of Your Life (1949), The Belles of St Trinian's (1954) and The School for Scoundrels (1960), as well as countless stage roles, may have looked effortless, but his preparation was painstaking. Naomi was always on hand to hear his lines, share his concerns and stand in as director.
After his death, when Naomi was in her sixties, her friend and agent Faith Evans talked her into writing not a biography - "because Alastair would have hated it" - but an autobiographical memoir, Dance and Skylark (1988), in which she was able to express the uniqueness of their partnership on her own terms, as well as her own radical views on many matters. She went on to write a series of articles about her life in the country for The Oldie magazine.
Naomi Plaskitt, author and actress: born Bedford 30 November 1913; married 1932 Alastair Sim (died 1977; one daughter); died Henley-on-Thames, Oxfordshire 3 August 1999.