Sidney Alderman Blackmer (July 13, 1895 – October 6, 1973) was an American Broadway and film actor active between 1914 and 1971, usually in major supporting roles.

While working as a construction laborer on a new building, he saw a Pearl White serial being filmed and immediately decided to pursue acting as a career.

[citation needed] He won the 1950 Tony Award for Best Actor (Drama) for his role in the Broadway play Come Back, Little Sheba, co-starring with Shirley Booth.

[citation needed] For his contributions to the film industry, Blackmer has a motion pictures star on the Hollywood Walk of Fame at 1625 Vine Street.

Among his most notable roles was the character of presidential candidate William Lyons Selby in the Outer Limits episode "The Hundred Days of the Dragon".