Why do we call someone who does things differently a “maverick”?

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 live-
stock. 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.