Robert Aaron Dean was born on December 29, 1836, near Chulahoma, Mississippi.[1] He was the son of Russell Dean, who was of English and Scottish descent; and his wife Louisa Ann (Alsup) Dean, who was of Welsh and Irish descent.[1] Dean attended the private schools of his native Marshall County, Mississippi, and became a farmer.[1]
In 1877, Dean was elected to represent Lafayette County as a Democrat in the Mississippi House of Representatives for the 1878–1880 session, and entered office on January 8, 1878.[3][1] Dean then represented the 7th District (Lafayette County) in the Mississippi State Senate from 1886 to 1896.[4][5] In 1890, Dean was elected by acclamation to the position of the senate's President pro tempore.[6] He was a delegate at the 1890 Mississippi Constitutional Convention and chaired the penitentiary committee that banned convict leasing.[1] In 1892, Dean was re-elected to the presidency pro tempore, defeating Senator John M. Simonton with a vote of 30 to 12.[7] His tenure as president pro tempore continued through the 1894 session.[8] In 1896 Dean was succeeded in the Senate by W. F. Love.[9] From 1900 to 1903, Dean was part of the Commission that supervised the construction of the new Mississippi State Capitol building.[1] On January 25, 1908, Dean was elected to replace George W. Hightower, who resigned, to represent the 32nd District (also Lafayette County) in the State Senate.[1] He was succeeded in the state senate by Lee M. Russell.
Dean was a Democrat, a Baptist, and a Mason. He married Lucy Ann Langston on February 2, 1864, and they had eight children together, all of whom were living as of 1908.[1] Their names were Russell Langston, Thomas Greenwood, Joseph James, Robert Aaron Jr., Louanner, Georgia, Minnie, and Hardy Mott.[1]
