Best duel Opponent for Ranger PC

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I'm a GM, and one of my PCs is an Orc Ranger. He will soon be returning to his old orc tribe to challenge the Chieftain to 1 v 1 combat for control of the tribe. What should I pick as far as class/feats/fighting style/etc to make the Chieftain a challenging and unique opponent?

The PC is:
- 18th level Ranger/2nd level Cleric/1st level Mammoth Rider
- Two-weapon fighter, wielding a pair of flaming short swords
- Gets 7 attacks per round, from feats and other stuff
- Animal Companion is an Arsinoitherium (neolithic Rhino) grown to size Huge. Will only be allowed in the duel if the Chieftain also has an animal helper of some kind.

The only necessity for the Chieftain is that he should be tough, grizzly, and Orcish in nature. I know rogues and swashbucklers and other flouncy Dex builds make great duelists, but they're just not Orcish enough. Also, the Chieftain is of Evil alignment, so no Paladins. His alignment could be Lawful/Chaotic/Neutral as needed.

Suggestions?

[Claxon]

Something with a lot of mobility, to deny the ranger full attacks will honestly give the character a lot of trouble. Don't stand toe to toe with the ranger and trade full attacks.

If the NPC will be 20th level, a mobile fighter is able to make a full attack as a standard action. The fighter need only let the ranger move up to him once and then move 10 ft away after full attacking as a standard. Rinse and repeat. The ranger will only get 1 attack, the fighter will get a full attack each time.