He had career spanning more than 55 years on Broadway with his first role as the title character in Elmer Brown, the Only Boy in Town in 1908/1909.
Perhaps his most memorable performance was as Teddy Brewster, a lunatic who thinks he is Theodore Roosevelt, in the 1944 classic film Arsenic and Old Lace opposite Cary Grant. He had previously portrayed that role in the 1941 Broadway play of the same name on which the film was based. He went on to play the "real" Roosevelt in the 1950 Bob Hope comedy Fancy Pants and reprised his role as Teddy "Roosevelt" Brewster in the 1955 TV adaption of Arsenic and Old Lace in the anthology series The Best of Broadway.
Among his other notable film roles, Alexander played Steve Edwards in A Tree Grows in Brooklyn in 1945, Mr. McComber in Summer Holiday in 1948, Jack Riker in Winchester '73 in 1950 and Howard Shipley in The Marrying Kind in 1952.
During the 1950s and early 1960, he guest starred on television series, such as The Phil Silvers Show, Adventures of the Sea Hawk and Car 54, Where Are You?.
Alexander's last performance was as Mayor Crane in the Broadway comedy Never Too Late, a role he had played since 1962.
- John Alexander Filmography