Also see What do you call a person who does/thinks the opposite of the crowd for just that reason? and How to describe someone who often has his own idea and judgment, where words such as the following are suggested.

• individualist, “Someone who does as they wish, unconstrained to external influences”
• strong-minded, “Having a vigorous, independent will and views”
• self-assertive, “determined to advance one's own personality or views”
• iconoclast, “One who attacks cherished beliefs” (etc.)
• contrarian, “a person who expresses a contradicting viewpoint, especially one who denounces the majority persuasion”
• opinionated, “Holding to one's own opinion obstinately, stubbornly and unreasonably”
• resolute, “Firm, unyielding, determined”

and per FumbleFingers, “nonconformist, renegade, maverick, rebel, radical, individualist, heretic, dissenter, dissident, iconoclast, loner, etc., etc.”

Also see What do you call a person who does/thinks the opposite of the crowd for just that reason? and How to describe someone who often has his own idea and judgment, where words such as the following are suggested.

• individualist, “Someone who does as they wish, unconstrained to external influences”
• strong-minded, “Having a vigorous, independent will and views”
• self-assertive, “determined to advance one's own personality or views”
• iconoclast, “One who attacks cherished beliefs” (etc.)
• contrarian, “a person who expresses a contradicting viewpoint, especially one who denounces the majority persuasion”
• opinionated, “Holding to one's own opinion obstinately, stubbornly and unreasonably”
• resolute, “Firm, unyielding, determined”

and per FumbleFingers, “nonconformist, renegade, maverick, rebel, radical, individualist, heretic, dissenter, dissident, iconoclast, loner, etc., etc.”