The axe man is a mysterious enemy who appears all of a sudden and attacks for no reason. However, you can learn of his identity through the various files and cut-scenes you receive during the "Flashback" scenario. He can withstand an exceptional amount of damage, therefore it is usually wiser to run and escape rather than stand your ground and fight. It is possible to drive him off when you deal enough damage, but this is only temporary and you can guarantee that he will be back.