Seems to really like messing with people. He has saved the world, defeated the strongest opposition there is available... but he's grown bored in the mundanity of the peace that he's created. He now spends his days tormenting Nazeem, stealing and hording cheese wheels, or any other thing that suits his fancy to provide even a moment's reprieve from boredom induced melancholy.

He's very bored, if someone offers him a challenge and he was even partially satisfied, he's unlikely to kill them.

The dragonborn rolls a d100 when the party is low health, on a high 90+ roll, he is filled with a murderous intent and intends on killing the entire party.
On a <90 roll the dragon born decides knocking the party unconscious so they can return stronger is the right play.
Someone in the party rolls a 1d6
1: The Dragonborn attempts to incapacitate all targets. And promptly leaves them in the street.
2: The Dragonborn offers the party the chance to stand down, with no more bloodshed. If they refuse, the dragonborn attempts to incapacitate all party members, and then proceeds to loot: 1 equipped item of the Dm's choice, and the player must roll 3d20, the dragonborn loots the item in their inventory that corresponds to the number. EX: if the player rolls a 5, the 5th item in their inventory gets looted.
3. The Dragonborn attempts to incapacitate all targets, and brings them to a jail house determined by a 1d10 roll.
1. Whiterun Hold: Dragonsreach Dungeon
2. Haafingar: Castle Dour Dungeon (Solitude)
3. The Reach: Cidhna Mine (Markarth)
4. The Rift: Riften Jail
5. Eastmarch: Windhelm Jail (Palace of the Kings)
6. The Pale: Dawnstar Barracks
7. Falkreath Hold: Falkreath Barracks
8. Hjaalmarch: Morthal Jail (Guardhouse)
9. Winterhold: The Chill
10. Solstheim (Dragonborn DLC): The Bulwark Jail (Raven Rock)

The players will wake up in a jail cell corresponding to the roll of the d10, and each player will have a 1,000 gold bounty if they choose to escape.
4. The Dragonborn smiles. "Seek me out again adventurers." Then proceeds to flee.
5. The Dragonborn attempts to incapacitate all targets, after incapacitating all targets, the party wakes up to find a note.
"You did well in fighting me, take this gift and grow stronger. Challenge me again."
The dragonborn leaves a dragonbone weapon of dm choice. Enchanted
2,000 gold (if less than 4 players, 3,000 if 6 players)
6. The Dragonborn attempts to incapacitate all targets.
Upon the party waking, they will find that they've been moved to another place, in front of them the dragonborn is cooking and eating by the campfire. The dragonborn will offer advice to each of the party members. The party members will be able to choose from the following permanent boons.
One free feat.
A once-per-long-rest reroll.
+1 to a saving throw.
A unique Thu'um-inspired ability.