Here's some dictionary definitions of the word "maverick":
- A lone dissenter, as an intellectual, an artist, or a politician, who takes an independent stand apart from his or her associates.
- One that refuses to abide by the dictates of or resists adherence to a group; a dissenter. (Am.Heritage Dict.)
- A person who acts independently of his political party or group.
- A masterless person; one who is roving and casual (that's the Shorter Oxford def.)
- One who departs from the customs and beliefs of his group. (Webster)