|The Lich King|
Prince of Darkness
After Ner'zhul created an unstable amount of portals across Draenor and attempted to escape via one, he was captured by the Deciever, Kil'jaeden. After his body was torn, his soul was left intact and alive, although not without the agreement of entering the service of Kil'jaeden again, even after Ner'zhul begged for death. Thusly, Ner'zhul was bound to the Frozen Throne, encased in ice from the reaches of the Twisting Nether and given the Deceiver's unfathomable dark powers, Ner'zhul became the first soul to be known as; the Lich King, and would rule the Scourge.
After the events between Ner'zhul and Kil'jaeden, the Lich King (Ner'zhul) was sent to Azeroth and landed in Northrend, where the ice he was incased in formed into the shape of a throne (now known as the Frozen Throne). He would form the Undead Scourge and control them from there as his central base of operations to weaken the world via his Scourge in preparation for the Burning Legion. Led by Tichondrius himself, Dreadlords were sent to watch over him as well.
Throughout time, the Lich King experimented in immoral ways with his new powers, enslaving the local life forms. The Plague of Undeath that came from his Frozen Throne turned each and every one of them into his undead servants. Paired with his army and necromantic powers, he was able to conquer much of Northrend. Over the course of time, harvesting more and more souls, his power also increased exponentially from when he originally became the Lich King. The Dreadlords sent to watch him became aware of this as well.
Some time in the future, the Lich King entered a war with the Kingdom of Azjol-Nerub. Lasting for ten years, this conflict was known as the War of the Spider. While the ancient inhabitants of Azjol-Nerub (the Nerubians) were immune to the Plague of Undeath, they were still able to be reanimated. The Lich King was reportedly impressed with his enemy, though still ended in triumph. As a testament to the Nerubian's tenacity and age, he took use of their architectural styles.
Once conquering the majority of Northrend, the Dreadlords sent to watch over urged him to proceed with the plan to prepare the world of the Invasion of the Legion. The Lich King then reached out to Azeroth and ensnare any dark soul that would hear his request. Kel'Thuzad, a Mage and well-known member of the Kirin Tor answered his call and was soon working with Ner'zhul as the first member of the "Cult of the Damned", a cult that would begin worshiping the Lich King as their god and teach Necromancy to aid the Lich King's undead armies more proficiently. Kel'Thuzad and Mal'Ganis, a Dreadlord, were instructed to begin paving the way for the Legion, yet the Lich King, aware of Kil'jaeden's schemes and plot, clandestinely sought a way out of his will-binding.
Attack on Lordaeron
After much preparation, Kel'thuzad and the cult released the Plague of Undeath upon the Kingdom of Lordaeron. Lovers Lady Jaina Proudmoore and Prince Arthas Menethil began to investigate this new threat.
Arthas himself fought the undead and even succeeded to kill Kel'Thuzad himself, yet the Undead Scourge continued to violently ravage throughout the kingdom, slaughtering every regiment of soldiers; both Lordaeronian and those from supporting nations.
The tides of events changed drastically when Arthas decided to slaughter the entire city of Stratholme in an attempt to prevent the plague from spreading further. His lover, Jaina Proudmoore was in strong disagreement with this decision and left him on his own - yet Arthas would continue, dead-set with his goal. This event was later known as the Culling of Stratholme and changed people's view on Arthas's humanity.
Arthas then set off for Northrend to destroy the very source of the plague, hoping to end its "leader", the Dreadlord Mal'Ganis. During his trip, he ran into his long-time friend, Muradin Bronzebeard who led him to a famous relic weapon that would help him combat the undead; yet Arthas fell to the Lich King's power.
Thinking that it'd save his people, Arthas took the cursed Frostmourne, an unholy runeblade. While granting him great power, the sword led to the supposed death of Muradin and Arthas began to lose his own very soul, becoming the first of the Death Knights.
In the end, Arthas managed to execute Mal'Ganis, yet as his soul and sanity were shattered, he led the Undead Scourge against Lordaeron - killing his own father, King Terenas Menethil II and brought Lordaeron to its knees.
Alongside Arthas as his mightiest champion, Ner'zhul continued to spread the plague throughout Lordaeron, causing the evacuation of the (surviving) citizens. Under the leadership of Uther the Lightbringer, the remnants of the Order of the Silver Hand fought back with valiance, yet failed in the end as even Uther fell before Arthas and Ner'zhul.
Next, by the will of Tichondrius, Arthas led his forces north to the Kingdom of Quel'Thalas to resurrect Kel'Thuzad, who was capable of summoning Archimonde into the mortal plane. While the forces of Quel'Thalas fought back alongside their allies within the Alliance of Lordaeron, Arthas ultimately decimated the kingdom - destroying their very capital, Silvermoon, and altering their beloved Sunwell to bring back Kel'Thuzad as a lich. This conquest was later known as the Scourge Invasion of Quel'Thalas and left the kingdom in shambles.
Following, Ner'zhul had his minions attack the magical city of Dalaran, at that time located within the Hillsbrad Foothills. Getting hands on a powerful spellbook (known as the Book of Medivh) which contained incantations capable of summoning Archimonde, the Scourge were finally capable of summoning him into their world. Archimonde was then summoned outside of Dalaran and passed the command of the Scourge to Tichondrius and the other Dreadlords. Although Archimonde relinquished Ner'zhul's leadership over the undead, he forgot to return the Frozen Throne to Kil'jaeden - allowing the Lich King to remain.
When the Legion invaded the kaldorei region of Ashenvale, Illidan Stormrage was released from prison by the Wardens following his ten-thousand year sentence. Due to Illidan's addiction to magic, Ner'zhul deployed Arthas to Kalimdor where he secretly told Illidan of the unfathomable power of the Skull of Gul'dan. Unable to resist due to his magical addiction, Illidan took the skull and consumed its power. However, the result of which caused him to develop physical demonic mutations - only something chaotic fel magic could muster. Just as Ner'zhul had planned, Illidan liberated Felwood and executed Tichondrius with his newfound strength - he was the first of the Demon Hunters. Due to the lack of support from Tichondrius and his elite forces, Archimonde's attempt to take over Mount Hyjal led to his inevitable "death" - all in Ner'zhul's plan. This course of events would be known as the Battle for Mount Hyjal.
With Illidan now roaming free, Kil'jaeden confronted him with an irresistible offer - to destroy Ner'zhul and put an end to the Scourge in exchange for further unimaginable power and a position within the high echelons of the Burning Legion. Illidan agreed and traveled to Northrend to destroy the Frozen Throne in which the spirit of the Lich King was held inside; which would put an end to the Lich King should it be destroyed. Via the knowledge gained from Gul'dan's memories in the Skull, Illidan sought out the Tomb of Sargeras, rumored to be situated on the Broken Isles, to claim Sargeras' remains. Illidan needed support, however, and used his demonic powers to lure the serpentine naga from the deep reaches of the sea. Led by Lady Vashj, her naga assisted Illidan in reaching the Broken Isles.
Illidan, now in possession of the Eye of Sargeras, ventured to Dalaran, which had a powerful concentration of ley-lines, allowing him to cast a chaotic, destructive spell from the Eye aimed towards Icecrown Citadel across the continent. The attack broken through the defenses of Icecrown and the Lich King had no counter against it - sure that he would be forever defeated on that day. In the final moments of the spell, however, Illidan was stopped by his brother Malfurion, the powerful archdruid, as Malfurion had sensed that the spell was causing much more damage to the world than just to the diabolical Lich King; letting Ner'zhul escape his ultimate demise by the grace of moments.
War Against Sylvanas
Given Ner'zhul had now directly defied the will and orders of the Legion and his masters within it, he knew that Kil'jaeden's merciless wrath would soon come for him. Additionally, Ner'zhul was losing his powers rapidly at this time as well - pushing Frostmourne from the throne caused a crack within the ice, and Illidan's decimating attack further worsened this. Arthas was also losing his powers, as he too drew from the Frozen Throne's might through his sword, Frostmourne, and his reign over the undead was also becoming looser.
Ner'zhul, desperate to save himself from the inevitable arrival of Kil'jaeden's men, he called upon Arthas, his mightiest mortal servant. Arthas, however, was leading the Scourge against a civil war in Lordaeron against approximately half of the other remaining Scourge, which the banshee queen Sylvanas Windrunner took over due to Arthas' power of the Scourge slipping. A third "faction" of Scourge remnants also remained, under the control of the three remaining officers of the Legion - Varimathras, Detheroc and Balnazzar. Due to Ner'zhul's desperation, Arthas had to leave the battlefield to assist his master and give command to his highest lieutenant, Kel'Thuzad. In his absence, Sylvanas ultimately took over the capital of Lordaeron with her rebel Scourge known as the Forsaken. The Forsaken left the standing city to ruins, however, and took home within the old sewers and vowed to put an end to the Scourge and drive Kel'Thuzad and his forces out.
Weakened but incredibly determined, Arthas arrived in Northrend for Illidan's naga and Sin'dorei waiting. He and his Nerubian allies proceeded to act against Illidan and his forces to get to the Frozen Throne and defend Ner'zhul. Arthas would eventually reach Prince Kael'thas Sunstrider, leader of the Sin'dorei, whom fought with his powerful elven runeblade, Felo'melorn; also reminding Arthas of his former beloved, Jaina Proudmoore, and that she now hated him in order to make him hesitate. Felo'melorn, which translates to Flamestrike, clashed against the unholy Frostmourne, but ultimately Sunstrider and his forces had to flee, leaving Arthas' path to the throne open. Opening the doors to the Frozen Throne, Illidan was awaiting Arthas - commencing a brutal battle between the two; Illidan's two warglaives and Frostmourne clashing. Illidan nearly defeated Arthas, however, accidentally left himself vulnerable in his final blow and Arthas took advantage, slicing open Illidan's chest - grievously wounding him and forcing him to collapse. Arthas didn't execute him, however, and proceeded up the gates of the Frozen Throne - warning Illidan to leave Azeroth and never return.
As Arthas proceeded up the stairs, he was invaded by voices of the past - Uther warning him that "If we allow our passions to turn to bloodlust, then we will become as vile as the orcs.", and other angry remarks from Uther and Muradin, and even his responses, yet ignored them and continued to progress up the icy stairs. Upon reaching the top, he was met with an icy cask, the Frozen Throne; within it was a suit of armor known as the Plate of the Damned, completed with the Helm of Domination. Now two voices spoke to him - Medivh's warning to Jaina, and the whisper of Ner'zhul.
Arthas then let the might of Frostmourne meet the icy throne, shattering it as it exploded - shards of the icy crystal scattered. With the helm at his feet, once worn by Ner'zhul, Arthas placed the unspeakably powerful artifact onto his head. "Now - we are one!", in unison Arthas and Ner'zhul spoke - in which moment, their spirits fused together into a single, powerful form, just as the Lich King had planned.
The Lich King now proceeded to fall dormant for many years within the icy throne as blizzards raged across Northrend and his minions built up the Icecrown Citadel below the Throne.
While he dreamed, the many personas in his mind—Arthas Menethil, Ner'zhul, and Matthias Lehner, the personification of the remnants of Arthas—fought for influence and ultimate control over the powerful entity.
The Lich King's Awakening
After several years of dormancy, Arthas finally awoke - his citadel constructed and Scourge ready to execute his will, as well as his newly trained death knights. He soon ventured to Sindragosa's Fall and raised the ancient dragon Sindragosa as a frost wyrm.
In an attempt to take down the Grand Alliance and Horde, Arthas sent out packages containing plague-tainted general imported goods, hoping to wipe out both factions by turning them into undead. This plan, however, did not fully succeed as healers from the newly formed Argent Dawn could cure this.
King Varian Wrynn and Warchief Thrall realized this imminent threat to humanity and mobilized the Alliance and Horde Military to station themselves in Northrend; sending the prestigious Seventh Legion and Kor'kron to station in the region. Highlord Tirion Fordring of the Argent Dawn also sent his forces to combat the undead.
The Scarlet Enclave
Acknowledging the threat of the anti-Scourge Scarlet Enclave, Arthas forged a new order of Death Knights to combat them (and for other means), which would be known as the Order of the Ebon Blade and lead by Highlord Darion Mograine per appointment by the Lich King.
The Assault on Icecrown
After combating the Scourge in various locations throughout Northrend, it was soon time to lay siege on the heart of the Lich King's operation - Icecrown Citadel. To determine whom would be part of the assault force, Highlord Fordring held a grand tournament open to both the Alliance and Horde, known as the Argent Tournament.
After determining whom would be placed on the task force, Highlord Fordring, Warchief Thrall, and High King Wrynn led the force. Facing many Scourge, ultimately they ended triumphant; reaching the Frozen Throne high above the skies, Tirion faced the Lich King head on, eventually slaying him. Arthas's Helm of Damnation came off in his final moments and saw a vision of his father, Terenas, whom told him that "no king rules forever".
Bolvar Takes the Crown
Following the Lich King's defeat, Highlord Tirion Fordring was met by Bolvar Fordragon, who spoke of how the Scourge would run rampant if they did not have someone to chain them. He then commanded Fordring to place the crown upon his head so that he may take up the task. Initially hesitant, Fordring did so and made Bolvar Fordragon the new Lich King, shortly after agreeing to keep the news secret, away from the world.
Article adapted from Wowpedia.