Alexander Dienst, Jr., dentist, historian, and antiquarian, was born in 1870 in St. Louis, Missouri, the son of Alexander and Augusta (Moller) Dienst. His father, who emigrated from Germany at age fourteen, was a doctor, dentist, and Union veteran of the Civil War. Young Alex attended Ozark College, Greenfield, Missouri, Ohio Wesleyan University, and Philadelphia Dental College. In 1889 he established himself as a dentist in Temple, Texas, where he practiced his profession intermittently until his death. He married Florrie Gooda at Temple on August 15, 1893; they had six children. He served as water commissioner at Temple, did volunteer work as a recruiting officer for the army and navy during World War I, and in 1917–18 was postmaster, under an appointment made by President Woodrow Wilson.
Dienst became an enthusiastic student of Texas history and a collector of books and source materials dealing particularly with the Texas Revolution. He found that his collection emphasized the history of the Texas Navy, and he determined to put in its proper light the important service of the navy in the establishment of the Republic of Texas. His study appeared in four numbers of the Quarterly of the Texas State Historical Association, beginning with the issue of January 1909 and later reprinted privately. In 1917 Dienst published in the Southwestern Historical Quarterly a significant collection of "Contemporary Poetry of the Texas Revolution," compiled mainly from Texas and New Orleans newspapers. For twenty years he was a member of the executive council of the Texas State Historical Association and from 1932 to 1935 served as president of the organization. During his later years he gave much time to the promotion of his specialty in free public lectures on what he called "the grand theme of the pioneers of Texas." Much of his great collection of Texana became a part of the library of the University of Texas.
Dienst was a Democrat and was elected a delegate to state conventions from 1914 to 1924; he served as secretary of the Texas Democratic delegation to the national Democratic convention in St. Louis in 1916. Though he was a supporter of prohibition, he was a close friend and supporter of Governor James Ferguson. Dienst belonged to the Methodist Episcopal Church, South. He died of pneumonia at his home in Temple on May 6, 1938.