Octaviano Zapata, highwayman, was a native of northern Mexico about whom little is known before the outbreak of the Civil War in the United States. He owned a small ranch in Texas, near Clareño, but was forced to flee to the Mexican town of Guerrero with his wife and three children after the Clareño massacre of April 1861. He was once associated with Juan N. Cortina and Antonio Ochoa and organized a band of men that included outlaws, deserters, and political refugees from both sides of the border. They conducted raids in both Texas and Tamaulipas, Mexico, in search of money, supplies, and munitions. By the end of 1861, they were renowned bandits, famous along the lower Rio Grande border. The Union Army benefited from Zapata's raids into Texas, since they forced Confederate troops to remain in the area rather than participate in the military campaigns in the east. Beginning in 1862, Union agents, called enganchadores, offered rewards to Tejanos and Mexicans who conducted raids: 100 pesos in gold and from fifty to 150 acres of land in Texas. Zapata and his men were among the first recruited, and they were provided with arms and uniforms and promised additional rewards after the war. There is evidence that Zapata also received encouragement and support from the United States consul in Matamoros, Leonard Pierce, Jr. He was also associated with Edmund J. Davis, a former district court judge in Texas, who was conducting Northern-sponsored military activities in the vicinity of Brownsville and Matamoros. For these reasons, and because his band of men often flew the American flag during its raids, Zapata's party was often referred to as the "First Regiment of Union Troops."
In early December 1862 Zapata's men attacked a Confederate supply train; three weeks later a train of three wagons en route from Fort Brown to Ringgold Barracks, escorted by five Confederate soldiers, was attacked at Rancho Soledad near Las Cuevas, and all but one of the Confederate escorts were killed. These activities were instrumental in bringing about the extradition agreement negotiated in February 1863 between Confederate general Hamilton P. Bee of Fort Brown and Governor Albino López of Tamaulipas. Under the terms of this accord, Mexican authorities invited Confederate troops across the border to assist in the pursuit of outlaw parties. In late August Zapata's men ambushed Mexican troops on the road between Guerrero and Mier, and the alcalde of Guerrero requested that Maj. Santos Benavides of the Thirty-third Texas Cavalry, a predominantly Tejano regiment, intervene. Benavides crossed the Rio Grande with seventy-nine men on September 1, 1863, and took up the pursuit of Zapata's party. The following day Benavides surrounded them near Mier. After a brief exchange of fire, the Zapatistas dispersed, leaving ten men dead, including Zapata.