Gillette's most significant contributions to the theater were in devising realistic stage settings and special sound and lighting effects, and as an actor in putting forth what he called the "Illusion of the First Time". His portrayal of Holmes helped create the modern image of the detective. His use of the deerstalker cap (which first appeared in some ''Strand'' illustrations by Sidney Paget) and the curved pipe became enduring symbols of the character. He assumed the role on stage more than 1,300 times over thirty years, starred in the silent motion picture based on his Holmes play, and voiced the character twice on radio.
His first Civil War drama ''Held by the Enemy'' (1886) was a major step toward modern theater, in that it abandoned many of the crude devices of 19th-century melodrama and introduced realism into the sets, costumes, props, and sound effects. It was produced at a time when the British had a very low opinion of American art in any form, and it was the first wholly American play with a wholly American theme to be a critical and commercial success on British stages. In November 1915 he was elected a member of the American Academy of Arts and Sciences.
