Maverick

To call someone a maverick today means that you see them as an independent person who thinks differently, and the term applies to many professions and fields. It is generally considered to be a positive nickname but it might also apply to someone who doesn't follow the rules or norms of a field.   

The origin of this eponym is Samuel Maverick, a cattle rancher in Texas in the 19th century. At the time, the law was that all ranchers had to brand their cattle - but Maverick refused. 

The dictionary, in North America, will say that a maverick can also mean an unbranded calf, which makes sense. 

Maverick was also an American Western television series from 1957 - 1962. It was a comedic western originally starring James Garner as Bret Maverick, a poker player moving through the 19th-century American frontier. 

James Garner as Bret Maverick and Jack Kelly as Bart Maverick, Link