The President cannot fire him.
What happened to William Sessions?
Wrong =>
But according to a 2014 report by the Congressional Research Service, there are no statutory conditions on the Presidents authority to remove the FBI Director. In other words, the President can indeed fire the FBI director.
http://heavy.com/news/2016/10/james-comey-fired-fbi-director-hillary-clinton-email-private-server-influence-election/
Yes he can!