Apologist

a-pol-o-gist (noun) Is someone who defends, argues or justifies some institution, cause, faith, policy.

It seems like it's common connotation is geared towards the defense of Christian faith, but the meaning can be generalized.

It also stands for someone who makes an apology.

Resources:
-en.wikipedia.org/wiki/Apologist
-wordnet.princeton.edu/perl/webwn