William Sydney Penley (19 November 1851 11 November 1912) was an English actor, singer and comedian who had an early success in the small role of the Foreman in Gilbert and Sullivan's Trial by Jury. He later achieved wider fame as producer and star of the prodigiously successful Brandon Thomas farce, Charley's Aunt and as the Rev Robert Spalding in several productions of Charles Hawtrey's farce The Private Secretary.

Penley began his stage career in 1871 in farce and was soon performing in musical theatre. From 1875, he appeared in several runs of Trial by Jury, making an impression when he became a replacement in the role of the Foreman of the Jury. Over the next decade, he steadily gained prominence in character roles in operettas and Victorian burlesque, playing in several of these at the Royal Strand Theatre and other London theatres. In 1879 he toured as the leading comic role of Sir Joseph Porter in H.M.S. Pinafore and in 1880 he visited the US in a tour.

In 1883 he made a great success as Brother Pelican in Falka, and the following year came what The Times called "his first triumph", as Spalding in The Private Secretary, a role that he repeated several times. In 1892, Penley created the title role in Charley's Aunt, which played for a record-setting 1,466 performances in London, and in revivals of the play. He retired from the stage in 1901 and managed the Great Queen Street Theatre until 1907. He was also one of the proprietors of The Church Family Newspaper.