Claimant to the throne of Alterac
Daval Prestor was a human noble.
Prestor was a tall, slim figure with black hair and clean-shaven hawklike features that were the subject of gossip among the ladies of Terenas' court. He also had a quick mind and a friendly, engaging manner that endeared him to all involved in the Alterac crisis. It was said that he even got a smile out of Genn Greymane, the normally dour king of Gilneas.
Beyond the Dark Portal
Prestor was a minor noble, dispossessed and without backing, who came from the north. He came from one of the most mountainous and obscure regions of Lordaeron after his tiny domain had been destroyed during the Second War by a dragon attack. He and a handful of his close family traveled by foot — no mounts, not even any servants or guards — to the Capital City of Lordaeron, where he presented himself to King Terenas. Prestor soon became an integral part of Terenas' inner circle. When debating on what to do with Lord Aiden Perenolde, the treacherous king of Alterac, right after the Second War ended, Prestor advised Terenas to depose Lord Perenolde and declare martial law in the Alterac region.
Day of the Dragon
Greymane, Thoras Trollbane of Stromgarde, and Daelin Proudmoore of Kul Tiras debated what should be done with Alterac, protesting Lordaeron's continued presence there. Greymane supported Perenolde's nephew in his claim for the throne of Alterac. Trollbane advocated dividing it between Lordaeron and Stromgarde. Realizing that neither situation was acceptable, and that Lordaeron could not simply annex it, Terenas — telepathically coerced by Prestor — believed that a strong leader trusted by the Alliance leadership should be put in place as King of Alterac, and he declared Lord Prestor as his choice to take that position. Terenas was even prepared to give Prestor the hand of his daughter, Princess Calia, in coming years as part of a marriage alliance between the new king of Alterac and the king of Lordaeron.
The Kirin Tor of Dalaran had their misgivings, however. The red dragon Korialstrasz — in his guise as Krasus, a member of the Kirin Tor high council — attempted to penetrate the chateau of Lord Prestor, setting off a very powerful spell-trap known as the Endless Hunger. The powerful energies maimed him, but Krasus was able to discover who he truly was. Two other members of the high council, Drenden and Modera, saw that Prestor was a complete blank magically, implying that he possessed great power — "possibly almost as powerful as Medivh", as Modera put it. The fact that the Alliance leaders, including the normally stubborn Greymane, had given Prestor their support, and the fact that King Terenas appeared to be leaving Dalaran out of the loop entirely, increased the Kirin Tor's suspicions about this unusual man.
Shortly after the battle of Grim Batol, Lord Prestor disappeared under unusual circumstances, his chateau abandoned, his servants gone. Rumors indicate he may not have been who he claimed, and that the nobles of Lordaeron may have even been under his control for a time.
In the RPG
Daval Prestor was the human form taken by the Dragon Aspect Deathwing, seeking to manipulate the Alliance so he could destroy it from within. He spent some time disguised as the human noble, infiltrating the royal courts of Lordaeron, and consolidating power in order to avenge himself upon the other dragon Aspects.
After Grim Batol — when the Aspects' lost powers were restored after the destruction of the Demon Soul — Deathwing went into hiding, thus precipitating "Lord Prestor's" mysterious disappearance. His true identity is known only to Krasus and Rhonin, though only Krasus knew the name that Deathwing had taken while in his human form.Katrana Prestor's relation to Daval Prestor is unclear. No version of Katrana's cover story has given exact details of how the persona is related to Daval Prestor, though it's speculated that she is Daval's daughter (since "Katrana Prestor" is the human disguise of Onyxia, the daughter of Deathwing).
While Prestor's backstory connects him as Aiden Perenolde's distant cousin, this link was a ruse to give the persona some clout.
Northern Lordaeron could be the location of Lord Prestor's land, although some sources say he came from Alterac or just "a domain in the north". Alternatively, he could have made the story up and arrived from anywhere. Day of the Dragon does speak of "northern vassals" during the time of Terenas's grandfather in regards to the successful negotiations about the borders with the elves of Quel'Thalas.