Hi! There are 4 pirate bosses.
1. Ron the Ripper
and it drops Ron the Ripper's Sabre 
2. Deadeye Devious
and it drops Deadeye Devious' Eye Patch 
3. Lethal Lissy
and it drops Lethal Lissy's Shirt 
4. Brutus Bloodbeard
and it drops Brutus Blodbeard's Hat 
With the 4 items you can obtain the addon 2 of Pirate outfits: 
