Revolutionary War veteran Robert Rankin was born in the colony of Virginia in 1753. He entered the service of the Continental Army in 1776 with the Third Regiment of the Virginia line and participated in the battles of Germantown, Brandywine, and Stony Point, as well as the siege of Charleston, where he was captured; he remained a prisoner of war until exchanged, at which time he received a promotion to lieutenant. On October 1, 1781, during a furlough, he married Margaret (Peggy) Berry in Frederick County, Virginia. He returned to active duty on October 15 and served until the war's end. Robert and Margaret Rankin had three daughters and seven sons, one of whom was Frederick Harrison Rankin. The family moved to Kentucky in 1784. In 1786 Rankin was named by the Virginia legislature as one of nine trustees for the newly established town of Washington, in Bourbon County (later Mason County), Kentucky. In 1792 he served as a delegate from Mason County to the Danville Convention, which drafted the first constitution of Kentucky. He also became an elector of the Kentucky Senate of 1792. The last mention of Rankin in Mason County, Kentucky, is in the 1800 census. The Rankins moved to Logan County, Kentucky, in 1802 and to the Tombigbee River in Mississippi Territory in 1811; the area of their home eventually became Washington County, Alabama. Four of the Rankin sons fought in the War of 1812. The family suffered a severe financial reversal around 1819–20, probably in conjunction with land speculation and the panic of 1819. In July 1828 Rankin first made an application for a pension for his Revolutionary War service.
In 1832 the Rankins moved to Joseph Vehlein's colony in Texas, along with the William Butler and Peter Cartwright families. Rankin was issued a certificate of character by Jesse Grimes on November 3, 1834, as required by the Mexican government. He applied for a land grant in Vehlein's colony on November 13 of the same year and received a league and labor in October 1835. The town of Coldspring, San Jacinto County, is located on Rankin's original grant. Rankin had the reputation of being a just and diplomatic man. He was a friend of Sam Houston, and his influence with the Indians in the region was well known. Houston reputedly called upon him in the spring of 1836 to encourage neutrality among the Indians during the crucial Texan retreat toward San Jacinto. Toward the end of 1836 Rankin became ill, and he and his wife moved to St. Landry parish, Louisiana, where he died on November 13, 1837. His body was brought back to the family home near Coldspring, in the new Republic of Texas, and buried in the old Butler Cemetery. In 1936 he was reinterred at the State Cemetery in Austin. His widow lived in Texas with her sons, William and Frederick, in Polk, Montgomery, and Liberty counties until her death sometime after December 1852.