Maverick
Etymology
From Samuel Maverick, a 19th-century Texas rancher who, by many accounts, declined to brand his cattle; unbranded strays came to be called "mavericks." The word passed from unbranded livestock to any person who refuses to be labelled or to run with the herd. The literal "unbranded" origin is a neat fit for the figurative sense.
noun · /MAV-uh-rik/
An independent-minded person who refuses to follow the crowd or established rules.
What it names
For the principled nonconformist — someone who belongs to a group yet refuses to be branded by it.
Example
She built her career as a maverick, ignoring the conventions of her field.
Related idea
A maverick breaks from the group on principle while remaining part of it; a pariah is cast out by the group entirely — self-chosen independence versus imposed exclusion.