Reginald Owen Morris (3 March 1886 – 15 December 1948), known professionally and by his friends by his initials, as R.O. Morris, was a British composer and teacher.
Morris was born in York. He was educated at Harrow School, New College, Oxford and the Royal College of Music (RCM) in London, where he subsequently became professor of counterpoint and composition. On the outbreak of World War I he enlisted in the Duke of Cornwall's Light Infantry, along with his friends George Butterworth and Geoffrey Toye. He became famous as an exceptional teacher of counterpoint, and wrote several texts including Introduction to Counterpoint (Oxford 1944), Contrapuntal Technique in the Sixteenth Century (Oxford, 1922), Foundations of Practical Harmony and Counterpoint, Volume 1 of The Oxford Harmony (1946), and The Structure of Music (Oxford, 1935). In 1926 he taught at the Curtis Institute in Philadelphia. In February 1915 he married Emmie Fisher, thus becoming brother-in-law to Vaughan Williams, who had married her sister Adeline.
His compositions have been overshadowed by his formidable reputation as a teacher. Students of Morris included composers Gerald Finzi, Sir Michael Tippett, Constant Lambert, Robin Milford, Anthony Milner, Edmund Rubbra, Bernard Stevens and Jean Coulthard. As a composer he wrote symphonies and other works for full or string orchestra, for string quartet, solo voice, chamber orchestra with winds, as well as voices.
He died in London in 1948.