Dr. Gary Habermas was not only one of own personal mentors during the time I was dealing with my own doubts, but he has come to be a personal friend of mine.  My Atheist co-host David calls Gary- "the Dean of Doubt", and I'd have to agree with that assessment as he helps various people deal with their doubts all the time and has even categorized three different types of doubts; i) Intellectual Doubts, ii) Emotional Doubts and, iii) Volitional Doubts.