Robert Addison Gillespie, merchant and soldier, was born on June 12, 1815, in Blount County, Tennessee, the son of Robert and Patsy (Houston) Gillespie. He moved to Texas in 1837, and he and his brothers, James Houston and Matthew Milton, in January 1838, formed a mercantile and land partnership in Matagorda. James furnished the capital for the enterprise, known as Gillespie and Brothers. By 1839 the Gillespies had moved to La Grange, established a mercantile store, and were buying Texas bounty-land certificates.
In 1840 Gillespie joined John Henry Moore's upper Colorado River expedition. In 1842 he participated in the battle of Salado Creek and was a member of the Somervell expedition. He enlisted in John Coffee Hays's Texas Ranger company in 1843 and served almost continuously with the unit until 1845. During his service with Hays, he fought in numerous Indian engagements and was severely wounded by an Indian lance in the battle of Walker's Creek in 1844.
After Gen. Zachary Taylor arrived in Texas in 1845, Gillespie formed a company of volunteers, enlisted into federal service, and helped to occupy Laredo. When Hays organized the First Regiment of Texas Mounted Riflemen in the Mexican War, Gillespie joined the regiment and commanded a company. During the battle of Monterrey, he was the first to reach the summit of Independence Hill. He was wounded at the assault on the Bishop's Palace, on September 22, 1846, and died the next day. His body was removed to San Antonio for burial. On April 21, 1856, the remains of Gillespie, along with those of fellow ranger Samuel H. Walker, were reinterred in the San Antonio Odd Fellows Cemetery.