Charles Keller (February 13, 1868 – September 16, 1949) was a United States Army Brigadier General and businessman.

[2] Keller graduated from the academy second of fifty-four in the class of 1890[3] and was commissioned a second lieutenant (ASN: O-331)[4] in the United States Army Corps of Engineers.

[5][7] In 1898, Keller was in charge of torpedo defence in the harbors of Charleston and Port Royal, South Carolina and later temporarily assigned to Rock Island again.

[6] As a member of the Niagara Falls Committee he was instrumental in bringing about more efficient production of hydroelectric power.

[6] From 1913 to 1916, he served as the Officer in Charge of Sea Coast Defenses for river & harbor improvements in the Mobile District, Alabama.

[9] From March 1918 to June 1919, Keller held the temporary rank of brigadier general[6] and served as deputy chief engineer for the American Expeditionary Forces.

[6] When he retired in 1943 he was 75 years old, the oldest Army officer to serve on active duty during World War II.