John Rufus Blocker, trail driver and rancher, second of the three sons of Abner Pickens and Cornelia Randolph (Murphy) Blocker, was born in the Edgefield district of South Carolina on December 19, 1851. The family moved to Texas in 1852 and settled near Austin. During the Civil War John helped drive ox teams to Mexico to avoid the Union blockade. He attended the Swan Coats School and Texas Military Institute, Austin, before 1871, when he entered the cattle business in Blanco County with his brother Bill. Seeing the demand for beef in the North, Blocker made his first trail drive to Ellsworth, Kansas, in 1873. Over the next twenty years he took longhorn cattle to buyers in Colorado, Nebraska, Wyoming, the Dakotas, and Montana, and was said to know every waterhole from the Rio Grande to the Yellowstone River. On the trail he used an inverted (backwards) seven brand, and his peculiar but effective mode of roping cows with a large loop came to be known among cowmen as the "Blocker loop." During one trip in 1885 with 25,000 steers, he and his brother Ab, who had joined the family business in 1876, were detained at Fort Supply (or Camp Supply) by Oklahoma and Kansas ranchers who would not allow them to go on to market because of the fear of Texas fever. After several appeals to the United States government, Blocker and George W. West, whose herd was also affected, finally obtained a cavalry escort to their destination. Soon afterward, the cow trails through Kansas were closed to prevent the disease from spreading.
In 1881 Blocker married Annie Lane of Austin; they had four children. At one time or another, and with various partners, Blocker owned ranches in Tom Green, Coke, Maverick, and Dimmit counties, including the Chupadero Ranch near Eagle Pass, and also land in northern Mexico. In 1893 the Blocker brothers made their last trail drive north when they delivered Harris Franklin's herd of 9,000 cattle to a buyer in Deadwood, South Dakota. In later years Blocker made his home in San Antonio, where he joined the Texas and Southwestern Cattle Raisers Association. He also helped organize the Old Time Trail Drivers Association and was elected its first president. He died at San Antonio on December 1, 1927, and was buried in Dignowity Cemetery.