Greetings and thanks for reaching out!
!!!SPOILERS AHEAD FOR OTHER PEOPLE PLAYING THANKS!!! Think of the long-haired indestructible badass as this game's Nemesis; if you don't see a boss health bar when he shows up, run. If you trigger his boss battle (which you will do as you advance through the mission), that's a different story.
If you're talking about how to actually beat the boss, use the metal boxes scattered around the room for cover, and roll profusely when he begins to charge. If he jumps into the air, keep moving and stay away from metal boxes, since if he lands on them he sends them flying with enough force to kill you.
Happy gunning! EDIT: Oh, and to answer your other question, they're exactly the same.
ATKMTN