This is an unmissable story achievement, obtained upon completion of the first mission.
*** Spoiler - click to reveal ***He's not too difficult, but I would recommend getting aerial rave, level 2 as your first upgrade during the mission. You can shoot him, but it does very little damage. Your best bet is to wait for him to attack and dodge it, and use the time between his attacks to jump up and use aerial rave on his face for maximum damage. When you've done enough damage, he will fall to the ground and you can go to town on him for a bit. When he gets up, he'll throw a boomerang type weapon at you. When the weapon is vertical, dodge to one side or the other. When it is horizontal, double jump and dodge while in the air to stay airborne for a bit to stay above it. After this section ends, repeat as you did in the first section, and he should go down easily.