Maverick

The term "Maverick" is coined after Samuel Maverick, an early Texas politician. Maverick was a POW of the Mexican army for a period. He is most well-known for steadfastly refusing to brand his cattle. As a result, the word maverick entered the English lexicon, meaning both an unbranded range animal as well as a slang term for someone who exhibits a streak of stubborn independence. Maverick's stated reason for not branding his cattle was that he didn't want to inflict pain on them. Other ranchers, however, suspected his true motivation was that it allowed him to collect any unbranded cattle and claim them as his own.

So Maverick was an old southwestern politician, former POW, who acted erratically and used his unpredictability to take credit for that which was not his? John McCain may be a true Maverick after all.