Gregorio Cortez Lira, a ranchhand of Mexican parentage, was virtually unknown until one summer day in 1901 when he and a Texas sheriff, pistols in hand, blazed away at each other after a misunderstanding. The sheriff was killed and Gregorio fled immediately, realizing that in practice there was one law for Anglo-Texans, another for Texas-Mexicans. The chase, capture, and imprisonment of Cortez are high drama that cannot easily be forgotten. Even today, in the cantinas along both sides of the Rio Grande, Mexicans sing the praises of the great "sheriff-killer" in the ballad which they call...