Maverick- One that refuses to abide by the dictates of or resists adherence to a group; a dissenter
Remember the eccentric Thomas Hobson of "Hobson's choice" fame. Looks like he's got company. In South Texas, lived a lawyer Samuel Augustus Maverick in the mid-nineteenth century (1803-1870) who took up cattle ranching not because he was a rancher himself but 'coz a client gave him 400 hundred heads of cattle in lieu of cash. In Texas cattle grazed on the open range, without fences to keep one herd separate from another, and thus there was much opportunity for theft and disputes over ownership. To identify their cattle, ranchers branded them.
But Maverick due to reasons unknown (could be laziness or the cruelty of branding animals) would not brand his cattle and some stories say that he lost a few of his herd to his unscrupulous neighbors who would brand his cattle as their own while other claim that he was influential (being San Antonio's mayor) and hence was able instead to claim that any unbranded calf was his.
Thus, the name maverick started to be applied to all cattle without brands and writers who heard the story decided to take it beyond cattle. What better word to use for a politician who was "unbranded" by a party label, not "owned" by special interests? In the same vein, maverick began to be used for artists who were independent in their thinking and later for anyone who can be called a dissenter.
Did you know: Dude has its origin in the Wild West too??
Source: The Merriam Webster Book of Word Histories, www.answers.com