A person opposed to war or violence, especially someone who refuses to bear arms or to fight, on moral or religious grounds.
Example:
Always a strong pacifist, in later life he took to promoting actively the cause of peace and nonviolence.
Pacifists have not always met with sympathy or understanding. Refusing to fight ever for any reason, or even just in a particular situation when the reasons for fighting seem clear to many others, calls for strong faith in one's own moral or religious convictions, since it has often resulted in persecution by those who disagree. The Quakers and the Jehovah's Witnesses are pacifist religious groups; Henry D. Thoreau and Martin Luther King are probably the most famous American pacifists.