John Robert Thomas, Sr. (October 11, 1846 – January 19, 1914), also known as J. R. Thomas, was a U.S. representative from Illinois. He was later appointed a U.S. district judge in the Indian Territory, which then encompassed most of the eastern part of present-day Oklahoma, serving from 1898 to 1901. After statehood, he served on the Oklahoma State Code Commission which was tasked with reviewing and editing the new state laws that had been hastily put together during the rush to statehood. After returning to his private law practice, he went to the Oklahoma state prison at McAlester to interview an inmate on January 19, 1914, when he was killed by three other inmates who shot him to death while escaping prison.