It was in Angels & Demons, his second novel, that Brown introduced the character Robert Langdon, named after the artist/philosopher John Langdon, a friend of Brown's father, and inspired by the religious historian Joseph Campbell, whom Brown saw interviewed on a television programme.
"I recall being impressed by Campbell's open-minded and unthreatening delivery, especially when he spoke about controversial topics like myths and untruths in religion," Brown wrote. "I recall thinking that I wanted my character Robert Langdon to have this same open-minded tone."
Yes, Langdon is the embodiment of open-mindedness, continually lecturing poor Sophie about how stupid, evil, and bloody is Catholicism, while showing himself to be an ignorant, arrogant pontificating professor. The resemblance to Campell is indeed striking. For more about Campbell and his dislike for Christianity, go here. Finally, if Dan Brown is a "commited Christian," as he apparently claims, why would he base his fictional hero on Campbell? For more about Brown, Langdon, and their negative views of Christianity, see some comments I made back in August 2004.