In 1957 he appeared in "Mary Stuart" at the Phoenix Theatre in New York City and in 1963 he appeared in "Troilus and Cressida" at the Stratford Festival in Stratford, Ontario, Canada. His other New York theatre credits are "King Lear" (1956), "The Devils" (1965–1966), "Serjeant Musgrave's Dance" (1966), and "Soldiers" (1968). Mr. Colicos' skill in acting resulted in his being chosen to play the title role in a memorable and first-ever production of "King Lear" (1964) at the Stratford Festival.