In the nineteenth century, Samuel A. Maverick was a stubborn Texas rancher who, because he said it was cruel, refused to brand his cattle even though it was the only way to identify who owned free-range livestock.
Instead he would round up all the unbranded cattle he could find, even those not from his own herd. At first any stray unbranded cow was called a “maverick,” but the word has grown to mean anyone Who doesn’t play by the rules.