Juan Nepomuceno Seguin was born into a prominent Tejano* family with close ties with Stephen Austin, leader of the first American settlers in Texas. ("Tejanos" = residents of Texas descended from Spanish-speaking settlers of Texas and northern Mexico)
Juan Seguin's mother was postmaster in San Antonio de Bexar, and his father helped write the Mexican Constitution of 1824. In 1825, Juan married Maria Gertrudis Flores de Abrego, a union that produced ten children.
Seguin, after serving as an alderman or city council member, became mayor or alcade of San Antonio in 1833. After Mexican President Santa Ana repealed the 1824 Constitution, Seguin joined the Texas Revolution or War for Independence and was commissioned a captain by Stephen Austin. He fought successfully in the Battle of Concepcion and joined the garrison at the Battle of the Alamo before leaving as a messenger to other Texian troops. By the time he returned with reinforcements, the Alamo had fallen.
Seguin later fought in "the Runaway Scrape" and was a cavalry officer in the Battle of San Jacinto led by Sam Houston, after which he was promoted to Lieutenant Colonel and represented Texas at the Mexican surrender at the Alamo.
Seguin signed the Texas Declaration of Independence and served as a senator for the Republic of Texas from 1837 to 1840. The new town of Seguin was named for him in 1841, and he again became mayor of San Antonio.
Few Anglos lived in San Antonio after the Texas Revolution of 1835–36 as Tejanos* continued their rule. Seguin's political situation became increasingly precarious because of the changing balance of power as Anglo "adventurers" moved to Texas for cheap land and fast money. Those Tejanos who remained in Texas often found their livestock and corn stolen; others had their land taken in disputes.
When the Mexican General Vasquez captured San Antonio in 1842, he announced that Seguin held loyalties to Mexico, leading Seguin’s enemies to denounce him as a spy. Seguin fled to Mexico, where he was arrested and forced to serve as a staff officer for the Mexican Army, later fighting for Mexico in the Mexican-American War, after which he settled again in Floresville, Texas.
In the 1850s he served as Justice of the Peace for Bexar County and County Judge for Wilson County before returning in 1883 to Mexico, where he died in 1890. His remains were returned to Texas in 1974 and reinterred in Seguin in 1976.
The writing and publication of the Personal Memoirs of John N. Seguin was part of his effort to set the story straight and appeal to Americans while also describing the conflicted position of Mexican Texans.
from http://historymatters.gmu.edu/d/6531/ (History Matters: U.S. Survey Course on the Web) and https://en.wikipedia.org/wiki/Juan_Segu%C3%ADn
Research Post on Juan Seguin by Carlos Zelaya, LITR 5431 American Romanticism spring 2013
Texas State Historical Association on Seguin
Texas A&M site on J. N. Seguin
Seguin Family Historical Society
Juan Seguin Monument in Seguin, TX