Brave New Films talks to the actual original Mavericks, who aren't too fond of John McCain using their name:
Fontaine Maverick, great-great-granddaughter of Samuel Augustus Maverick (1803-1870) explains the origin of the expression -- and why it shouldn't apply to the Republican candidate:
Samuel Maverick was a Texas cattleman, land baron and politician, so influential that he was one of the signers of the Texas Declaration of Independence. Fiercely independent and equally liberal. Sam became well known for what he didn't do, however. It seems, according to Fontaine, that he had taken some cattle in lieu of a debt he was owed. He let them roam on an island off of Texas, and for whatever reason, didn't brand them. So, any unbranded cattle became known as Maverick's. Now, this more than likely wasn't an act of revolt. No one knows for sure, but Maverick really wasn't much of a cattleman. He was also shrewd, later on in life if cattle weren't branded, he would often claim them.
Sam was also very spirited and free minded. It was because of this that in 1867 the term Maverick was first cited as being used to describe someone with an independent streak, someone not branded.
"Mavericks believe everybody has a right to be in America so long as they obey the law," Fontaine told me. "Grandfather Maury was no coward. He chased the Klan right out of San Antonio once, stood up to the mob... Maury was burned in effigy in San Antonio, for his defense of members of the Communist Party's right to assemble, for his defense of the Hispanic community, support for those who didn't have a voice. "
"My brother called me from California last week during the VP debate and told me if they said the world Maverick one more time, he was going to shoot the TV. Of course, he doesn't have a gun, but, you get the point. My mother was just quoted in the New York Times about how we feel McCain is branded, Palin is branded, they are Republicans, and true Mavericks carry no brand. It's driving our family crazy, upsetting us and the legacy of my family, and we really with the campaign would stop misusing the word and the phrase.
"John McCain on a few occasions has shown that he can go against his party, but how hard is that when his party has been wrong on so many things as we now see," she continued. "But he has a brand. And Palin, I'm not sure she even knows the history of the word of or my family, but one thing is clear to all of my family, she truly is not a Maverick."