Kenneth Griffith was born Kenneth Reginald Griffiths in Tenby, Pembrokeshire, on 12 October 1921. His parents separated within six months of his birth, and he was raised by his paternal grandparents, Emily and Ernest, staunch Wesleyan Methodists who instilled in him a lifelong habit of questioning authority. Before he left school, his headmaster suggested he drop the final "s" from his surname so that it would sound less English, advice the young Griffith took, and kept for the rest of his career.
Griffith made his first professional stage appearance in 1937, cast as Cinna the Poet in a modern-dress production of Julius Caesar at the Cambridge Festival Theatre. He was conscripted into the Royal Air Force during the Second World War, and afterwards joined the Old Vic company, going on to appear in more than eighty films over the following decades, frequently in unsympathetic character roles that made full use of his sharp, watchful screen presence.
His film and television credits include Jenkins in the Peter Sellers comedy Only Two Can Play (1962), the medic Witty alongside Richard Burton in The Wild Geese (1978), and appearances in both the 1955 film The Prisoner and the classic 1967-68 ITC television series of the same name, in the episodes "The Girl Who Was Death" and "Fall Out." Late in his career he played the cantankerous Reverend Jones in The Englishman Who Went Up a Hill But Came Down a Mountain (1995), a film set in a fictionalised Welsh village.
Griffith was equally well known as a combative and often controversial documentary filmmaker. A dedicated historian of the Boer War with a strong sympathy for the Afrikaner cause, he wrote, produced and performed all the roles himself in the acclaimed documentary series Sons of the Blood: The Great Boer War, 1899-1902 (1971-72), building on an earlier 1967 BBC film, Soldiers of the Widow. He published his autobiography, The Fool's Pardon, in 1994.