Apostate (Noun): A person who renounces a religious or political belief or principle. This definition perfectly matches the sentence, as Dr. Kevin has rejected all his religious and political beliefs.

Alchemist (Noun): A person who practices alchemy, especially one who sought to turn base metals into gold. (Incorrect meaning).

Anarchist (Noun): A person who believes in or tries to bring about anarchy (absence of government and law). (While Dr. Kevin rejected political beliefs, apostate is the broader term for rejecting core beliefs, covering both religious and political principles).

Apostle (Noun): A vigorous supporter or advocate of an idea or cause; often specifically one of the twelve main early followers of Christ. (Opposite meaning).