Gregorio Cortez Lira was born on June 22, 1875, in Matamoros, Tamaulipas, Mexico. He was the son of Roman Cortez Garza, a rancher, and Rosalia Lira Cortinas. When Gregorio was twelve years old, his family moved to Manor, Texas, near Austin, in 1887. Two years later, he began working with his older brother, Romaldo Cortez, on various farms and ranches in South Texas. They found seasonal jobs as vaqueros, which are cowboys, and as farmhands.

Gregorio eventually married Leonor Díaz, and they had four children together. After eleven years of working as cowboys and farmhands, Cortez and Romaldo established a farm in Karnes County, renting land from a local rancher. During his lifetime, Gregorio learned English and owned horses, which were important for his work.

In 1903, Gregorio divorced Leonor. Two years later, he married Estefana Garza, but this marriage did not produce any children and they eventually separated as well. At this time, many Mexican Americans in Texas, like Cortez, worked as agricultural workers or tenant farmers. The arrival of Anglo settlers and the railroad changed the political and economic landscape of the region, pushing Mexican Americans into lower social and economic positions. Despite these challenges, Cortez continued to work in farming and raised his family in South Texas.

On June 14, 1901, an incident occurred involving Gregorio Cortez, which set off a series of events leading to his flight from law enforcement. Sheriff W.T. Morris and his deputy, Boone Choate, arrived to question Gregorio and his brother, Romaldo Cortez, about a horse trade. During the questioning, a misunderstanding about the trade escalated tensions. The Sheriff's questioning was based on information from a man named Villareal, who had previously admitted to trading a horse for a mare owned by Gregorio. Choate misinterpreted Gregorio's response about the trade, leading to the Sheriff deciding to arrest the Cortez brothers.

As the situation heated, a confrontation ensued. The Sheriff drew his gun first and began firing at Romaldo, who was trying to help Gregorio. In defending himself and his brother, Gregorio shot and killed Sheriff Morris. This event marked the beginning of a manhunt for Cortez.

After the shooting, Cortez attempted to take his injured brother to Kenedy, Texas, for medical help. They struggled to travel, but Gregorio eventually reached the town, leaving Romaldo for care before fleeing north to hide at a friend’s ranch in Belmont, Texas. However, law enforcement soon discovered his location, leading to the Battle of Belmont.

In the early morning of June 15, 1901, Sheriff Robert M. Glover and his posse surrounded the Robledo ranch, where Cortez was hiding. A gunfight erupted between Cortez and his friends defending the ranch against the approaching lawmen. During the confrontation, both Sheriff Glover and a posse member named Henry Schnabel were killed. Cortez managed to escape the firefight and continued his flight.

For over a week, Cortez eluded a large posse, sometimes numbering up to 300 men. He traveled extensively, creating false trails and blending into towns to evade capture. He rode multiple horses, but after exhausting his mounts, he grew increasingly desperate. By June 20, 1901, he arrived in Cotulla, where he sought food and new clothing from locals while remaining unnoticed by authorities.

Ultimately, Cortez was captured on June 22, 1901. Following his arrest, he faced a series of trials. His first trial occurred on July 24, 1901, in Gonzales, Texas, where he was charged with the murder of Sheriff Morris. The trial was controversial due to a largely Anglo jury and significant community tension.

Over the next few years, Cortez faced numerous trials and legal battles. He was sentenced to death for the murder of Sheriff Morris, but the Court of Criminal Appeals later reversed this decision due to issues of prejudice during the proceedings. Cortez also faced charges related to the murder of Sheriff Glover, ultimately leading to a life sentence.

Efforts to obtain his release were initiated, and in 1913, Cortez received a conditional pardon after spending several years in prison. After his release, he relocated to Nuevo Laredo, Mexico, and later returned to Texas, where he lived with his family until his death on February 28, 1916. The cause of his death remains disputed, with possibilities of natural causes or poisoning by enemies. He was buried not far from where he had lived.