From Word.com comes the history of the word Maverick:
After the Republican Convention in early September, maverick made its way into our most looked-up words list. The applicable definition of maverick is unambiguous: "an independent individual who does not go along with a group or party." But the etymology and the original definition hint at a story worth repeating.
The man whose name has entered our political lexicon was a south Texas lawyer named Samuel A. Maverick, a member of a politically liberal family in the mid-19th century. A client once paid Maverick with 400 head of cattle, but since Maverick was not a rancher, he left the cattle unbranded and in the care of one of his men. After neighboring cattlemen helped themselves to the unbranded cows, the term maverick came to name any unbranded cattle, particularly a motherless calf.
Maverick then developed the extended meaning "a rootless wanderer." Americans traveling abroad carried that sense with them, and it was soon adopted into British English. In 1890 Rudyard Kipling titled a short story about small farmers, shoeless vagabonds, and night raiders The Mutiny of the Mavericks.
At about the same time, maverick was being used to label a member of a group who refused to accept one or more policies espoused by the group. So you might say that a maverick is one unwilling to be branded by the labels of a group.