Foster was born August 21, 1875, in Warrensburg, Missouri, the son of James Madison Foster and Agnes Johnson Eads, his father dying when he was just three years old. He went to public schools in Warrensburg, and then to the University of Missouri in Columbia and Washington School of Dentistry in St. Louis, Missouri. He took postgraduate work at the University of Southern California.[1]
In 1898 Foster volunteered for hospital service in the Spanish–American War and afterward helped in setting up the United States Army Dental Corps, being commissioned as one of the first dental surgeons in the U.S. Army in 1902. He served in that capacity until moving to Los Angeles the same year, where he practiced dentistry until he retired in 1924. After leaving the City Council in 1929 he worked in real estate.[1]
Foster was married first to Alicia C. Stepper in 1897 in Springfield, Kentucky, by whom he had three children, Martha, Douglas Jr., and Jane.[1] He married Margaret O. Montgomery in an Episcopal ceremony on September 2, 1927, with Los Angeles City Council Member Arthur Alber as best man.[2]
He died on July 22, 1962, in his home at 421 S. Bixel Street, leaving his widow, Margaret O., a son, Douglas F. Foster; a daughter, Jane Foster Morris; and a sister, Mrs. Frank W. Taggart. Although in 1927 he was a member of the Wilshire Boulevard Christian Church,[3] his funeral service was a requiem mass at the Roman Catholic Church of the Immaculate Conception in Los Angeles.[4]