This is a quest in a chain of 23 that runs pretty much all over the map.
However, it all starts with the Fallen Hero of the Horde.
(Hat tip to Xeir for the initial connectors between chains.)

Technically, it's four chain quests that tie into each other:
Chain 1:
1. Fall From Grace
2. The Disgraced One
3. The Missing Orders
4. The Swamp Talker

Chain 2:
1. Petty Squabbles
2. A Tale of Sorrow
3. The Stones That Bind Us
4. Heroes of Old
5. Heroes of Old

Chain 3:
1. Kirith
2. The Cover of Darkness
3. The Demon Hunter
4. Loramus
5. Breaking the Ward
6. The Name of the Beast
7. The Name of the Beast
8. The Name of the Beast
9. Azsharite

Chain 4:
1. The Formation of Felbane
2. Enchanted Azsharite Fel Weaponry
3. Return to the Blasted Lands
4. Uniting the Shattered Amulet
5. You Are Rakh'likh, Demon

Completing the entire chain gives you the following:
103,685XP at appropriate level
Shard of Afrasa
Enchanted Azsharite Felbane (Dagger, Sword or Staff)
Necklace of Sanctuary
Demon's Blood
Demon Hide Sack

The demon hunter is located in island in Ashara coords: 61,66

i went to the fallen hero of the horde, i spoke with him he didn't give me the quest , anyone knows why?
and thank u

Now this is actually an incredibly long quest line that has you killing lots of mobs and bosses here in Blasted Lands, in Azshara, and then back to Blasted Lands again, ending with a quest to kill Razelikh the Defiler. Now Anonymous doesn't have the whole quest line linked together, and some of the rewards are missing, but here's the full line as close as I can make it:

Step 1 (Alliance only, Horde just go straight to Step 2, far as I know):
Giver: Ambassador Ardalan
Name: Petty Squables
Description: Talk to the Fallen Hero of the Horde, who can be found at the border of Blasted Lands and Swamp of Sorrows

Step 2:
Giver: Fallen Hero of the Horde
Name: Fall From Grace
Description: Talk to the Fallen Hero of the Horde.

Step 3:
Giver: Fallen Hero of the Horde
Name: A Tale of Sorrow
Description: Go through the story of the Fallen Hero of the Horde in his chat dialog.

Step 4:
Giver: Fallen Hero of the Horde
Name: The Stones That Bind Us
Description: Destroy 3 Servants of Sevine, Servants of Allistarj, and Servants of Grol, and 9 Servants of Razelikh. The process by which to destroy them is to attack them until they become "banished" - they go all ghostly and translucent and are invulnerable, then destroy the stone near them. Be sure to initiate the attack while near the Servant's Binding Stone, otherwise, you will not be able to destroy it.

Step 5:
Giver: Fallen Hero of the Horde
Name: Heroes of Old
Description: Talk to Corporal Thund Splithoof, another ghost who will now spawn a few feet away, on the other side of the road from the Giver: Fallen Hero of the Horde.

Step 6:
Giver: Corporal Thund Splithoof
Name: Heroes of Old
Description: Open the chest that spawns on the ground next to Corporal Thund Splithoof. You'll get Shard of Afrasa from the chest as a reward.

Step 7:
Giver: Fallen Hero of the Horde
Name: Kirith
Description: Find Kirith the Damned in the cave in the eastern wall of Serpent's Coil. He's a 55 Elite freakin huge Felhound. Kill him, and the Spirit of Kirith appears. Talk to him to complete the quest and begin the next part.

Step 8:
Giver: Spirit of Kirith
Name: The Cover of Darkness
Description: Go back to the Fallen Hero of the Horde.

Step 9:
Giver: Fallen Hero of the Horde
Name: The Demon Hunter
Description: To come when I complete it!

Are there any other rewards besides exp and the +5 health/mana regen trinket?

Thank you for the info..:D

Please read my comments under The Disgraced One quest for complete quest line and rewards of the entire saga (total 5).