Willheim was born in Kirin'Var Village to Audlin Froststrike and Claudia Froststrike during the Second War. Before the destruction of Draenor, Audlin took Willheim to Azeroth, to protect him from Urlim the Unforgiving, and put him in the orphanage at Dalaran without telling him that he was his father. Audlin still raised Willheim in secret, acting as a teacher and a father figure. His childhood was a happy one, given that he had many friends, even among the older mages (including Antonidas himself.)
Third Person Speaking
Willheim speaks in the third person due to a magical experiment gone bad. The nature of the experiment has never been explained yet, but it has permanently warped part of Willheim's brain, causing him to speak in the third person, much to the annoyance of some.
During the Scourge invasion of Dalaran, Willheim was fleeing from Arthas and became trapped in an outhouse, which Arthas then lit on fire. The combination of plagued vomit in the outhouse, and negative energy coming from Arthas, warped Willheim's spirit, causing it to burn, making him run around the plaguelands on fire for five years, until he finally stopped in the Shadow Grave. He realized he was now one of the undead, and that everything he loved was totally destroyed.
Present Day Willheim
Death has... changed... Willheim. Some would argue that it is for the better.
In a ghostly form, Willheim requires a physical human body to inhabit. Without it, he cannot do anything physical. It has to be a perfect human size so that his ectoplasmic structure can fit. If it is too big, it will inhibit his movement. If it is too small, the body will rupture. Willheim only possesses the bodies of people who "do not deserve them." This usually means the Cult of the Damned, though he has been known to possess Human Venture Co. workers and other assorted ne'er-do-wells.
Undeath gave Willheim a new perspective on the Horde that he thought he knew everything about. He also saw tauren for the first time (they weren't in the Eastern Kingdom yet) which were both fascinating and cute in his opinion... but mostly cute. He has a tendency to pet, hug, or snuggle any tauren he meets.
Retribution against the Scourge
As soon as Willheim was able, he took his long-awaited fight to the Undead Scourge in what was left of Lordaeron. When it could be helped, he ignored the Scarlet Crusade, the Alliance, and the Mossflayer Trolls, focusing primarily on the Scourge. When he finished his fight against the scourge, he broke Audlin's silver staff on the Nerubian Overseer, revealing a note inside the staff that Audlin wrote before his death at Dalaran.
Today Willheim is in Northrend, his agenda not so much being vengeance as it is the "preservation of Dalaran and it's people."
Urlim the Unforgiving and Kael'thas
As soon as Willheim returned to Kirin'Var Village, he saw it lying in ruins and learned that his mother was not only killed in the siege, but a Shadow Council Warlock named Urlim the Unforgiving (originally of the Laughing Skull Clan) had ripped Claudia's soul out of her body and kept it ever since. Enraged and saddened by this, Willheim assaulted Tempest Keep numerous times in search of Urlim. However, Urlim was not there -- he had gone to Quel'Danas with Kael'thas to assist in the summoning of Kil'Jaeden. When Willheim learned this, he went to the island, found Urlim, and killed him at the armory by pushing him from a ledge and impaling him on a flagpole.
With the Soul Shard containing Claudia Flamestrike, Willheim went to O'ros the Naaru of the Exodar to have his mother's soul released. The Naaru's help was not unconditional, however. Willheim had to restore the limbs, and eyesight, of three of Kael'thas Blood Elves whom he had maimed at the Manaforges in his blind rage.
That being done, Willheim had another enemy to fight -- Kael'thas. True, it was Urlim that killed his mother, but it was Kael'thas that destroyed his true home and hundreds of innocent mages. One day, when Willheim is finished in Northrend, he will return to Quel'Danas and take his vengeance on Kael'thas once and for all.
Willheim is brave, but emotionally sensitive, sometimes to the point where his sadness nearly cripples him for a short time. His tears, whether they be of joy or sadness, burn whatever skin he is currently occupying. When this sadness wears off, anger might follow. An Angry Willheim is a thing of nightmares, bellowing smoke from his exposed ribs, flames burning in his eye sockets, and charred fists clenched as his smoking mouth snarls death threats. Even in this violent state, there is still time to reason with him before he starts burning people alive.
He is not above thanking others for their assistance, such as when he was taken prisoner by a goblin ghost-catcher and later rescued by a tauren. He even rewarded her with a "conjured hero cookie," a large chocolate chip cookie about half a meter in radius with a pink icing around the side.
Willheim has a very strict moral code, such as not killing civilians regardless of who ordered him to do it. Upon being ordered to attack Ambermill, Willheim refused, declaring he would have no more of the Forsaken's questionable agenda. He tries his best to remain neutral in the war between the Horde and the Alliance, focusing on "bigger fish" (i.e the Scourge.) He will always aid a friend in dire need if physically possible. He tries to be merciful, but there are some people, in his opinion, that deserve nothing less than a "premature cremation," such as the criminals in Dalaran's Underbelly. Willheim was quoted as saying he'd like to "Flood the sewers and flush these criminals out."
Willheim still honors old allegiances and relationships, but does not take kindly to betrayals. Upon encountering Fred Tomber, an old friend from Dalaran, in Stratholme and learning that he was one of the Thuzadin, he killed him without hesitation, pouring all of his rage into his fists as he smashed Fred's face into the cobblestone.
Willheim now spends his time in Dalaran with one Lawrence Fontane. This ten year old human boy was once a street urchin living in the underbelly of Dalaran, stealing food, valuables, and the like to get by. His cut was split with an older human named Garon, who would abuse Lawrence for accidentally damaging goods, such as Willheim's broken staff (which was already broken.) When Willheim noticed the boy stole his staff, he chased him into the sewers were he found Garon beating the boy. Willheim liberated Lawrence, and Garon was arrested and taken to the Grinder - Dalaran's prison for common criminals.
The whereabouts, or status, of Lawrence's parents are unknown. They are presumed dead.
There is an Alliance character named "Fontane," who is, indeed, supposed to be Lawrence.