I want a term for someone who generally doesn't care about their individual popularity or how other's view them and as such is willing to break social expectations about behaviors and do their own thing, even hen doing so may affect how other's view them. So something close to the phrase "Marches to their own drum", but I'd prefer something more concise and possible less colloquial.
I don't want a term that implies one is incapable of understanding societal expectations, I prefer the implication be a choice or lack of desire to try to fit expectations rather then an inability to do so.
I also do not want to imply a willingness to harm other's as a result of ignoring social expectations, via causing someone embarrassment, hurting feelings, or general rudeness for example. The term should focus on situations where ignoring of expectations would mostly only affect the person ignoring them, not when doing so is likely to harm others.
I'm okay with, and may even prefer, if the term comes with a implication that the person is less popular, less understood, or even mildly ostracized as a result of their ignoring social expectations.