"Welcome to the future. A pity you are too late to stop it. No one can stop me now! Selama ashal'anore!"
was the son of Anasterian Sunstrider, the last King of Quel'thalas, and prince of Quel'thalas. During the Second and much of the Third War, Kael'thas was a member of the Six, the leading council of the Kirin Tor, and ruling body of the nation of Dalaran. It was in Dalaran that the first of the many crimes that Arthas Menethil commit occurred: he won the hand of Lady Jaina Proudmoore who Kael'thas totally had a huge crush on. UNFORGIVABLE.
Kael'thas remained in Dalaran for much of the Third War, until news of the Scourge attack on Quel'thalas, the destruction of Silvermoon, death of his father, and the corruption of the Sunwell reached them. Another unforgivable transgression against him committed by Arthas Menethil! Kael'thas, concerned for the fate of his people, abandoned Dalaran shortly before the Scourge showed up there, stormed the place, and summoned Archimonde
who promptly wrecked the place
Arriving in Quel'thalas, Kael'thas was able to rally the survivours and took charge of the situation. Realizing that the corrupted Sunwell was a serious risk to his people, Kael'thas destroyed it. While he solved the problem of his people dying and going mad by consuming tainted magic, he now had to deal with the problem of his people dying or going mad because of magic withdrawal. Kael'thas renamed his people the Blood Elves, in honour of those who had fallen to the Scourge. While Kael'thas, as heir to the throne of Quel'thalas, could have claimed the throne and title of King, he chose not to, styling himself as the Lord of the Blood Elves instead. He also named some guy
to act as regent while he was away.
Realizing that his people needed allies to help them through these troubled times: the Scourge was still a serious threat and Arthas Menethil was still alive. Kael'thas reached out for help from his old allies: the remnants of the Alliance of Lordaeron. Unfortunately for Kael'thas, the highest ranked commander still alive in Lordaeron was Grand Marshal Garithos
. Though competent, Garithos' demeanor and dim view on non-humans left much to be desired. Still, despite their mutual loathing, the Alliance remnants were successful in freeing Silverpine Forest and Dalaran from the Scourge. However, the relationship between Garithos and Kael'thas soon became quite tense, as Garithos becaming increasingly nervous of that naga witch Kael'thas kept hanging around with. Certain that treachery was afoot, Garithos promptly locked Kael'thas and his Blood Elves in the dungeons of Dalaran.
Somewhat of a low point.
With some help from Lady Vashj
, Kael'thas was able to escape the dungeons, and rescue his troops. Desperate for some way of escaping Garithos, and finding a way to feed his people's thirst for magic, Vashj offered him a solution to both: travel to Outland, and seek out her master, the former Night Elf, Illidan. Looking the best option of his choice of bad options, Kael'thas agreed. Making use of the portal Kel'thuzad had opened to summon Archimonde, Kael'thas, Lady Vashj and their Blood Elf and Naga forces were able to escape into Outland.
After helping Illidan with a pesky Night Elf Warden-shaped problem, Illidan was happy to recruit Kael'thas and his Blood Elves, and promised to teach them all sorts of nifty tricks for acquiring magic. Furthermore, Illidan hated Arthas just as much as he did. Truly, it was an alliance that would last the ages. Together, the Illidari took control of Outland, dethroning its current lord, the pit lord, Magtheridon, and secure the Black Temple for themselves. They were now the unchallenged masters of Outland, with a safe home for everyone, plenty of magic for all, and totally safe from Kil'jaeden ever finding Illidan and berating him for his failure to destroy the Lich King.
Naturally, that was when Kil'jaeden, full of fire and fury, showed up and asked Illidan why the Lich King was still not destroyed. Suitably inspired, they set to work. While they tried their best, and poured their hearts into it, their attempt to kill Arthas, destroy the Lich King and not earn Kil'jaeden's eternal ire failed. In defeat, they returned once more to Outland, where Illidan bunkered down and prepared for the worst the Burning Legion had to offer.
While Illidan prepared to go full out paranoid, Kael'thas turned his attention to his own projects: namely helping his people deal with their addiction to magic. While Illidan was quickly becoming a reclusive, paranoid madman atop the Black Temple, was true to his world, proved to be quite knowledgeable about magic, both arcane and fel, and gave Kael'thas the techniques he needed to sate his people's hunger. He sent a group of his followers back to Quel'thalas to help spread knowledge of these techniques. Kael'thas himself, however, chose to remain in Outland, certain that the shattered remnants of Draenor held secrets that could further help his people.
Kael'thas' patience was rewarded when a fleet of five dimensional ships appeared in Netherstorm. Commanded by the Naaru, allies of the Draenei, they'd come to help them and fight the Burning Legion. Kael'thas and his forces were quick to seize control over the dimensional ships, and claimed the flagship, Tempest Keep, as his new headquarters. However, Draenei forces led by Velen the Prophet were able to reclaim one of the ships, the Exodar, and escaped with it to Azeroth. Despite Kael'thas efforts, he was unable to reclaim it. Not that it mattered, the Draenei crashed it into the side of a mountain anyway.
Even with just four out of five of his new dimensional ships, not to mention the naaru pilot, M'uru
they'd captured, Kael'thas was feeling pretty good about himself. He had M'uru sent to Silvermoon, certain that the crystalline creature's light based magic would prove to be a powerful source of magic for his people. He then set about reverse engineering the naaru technologies, and set about building a series of manaforges throughout Netherstorm, and totally wiped out Kirin Tor village on his doorstep, 'cause who cares about old allies, right? Everything was going so well that he almost didn't care when he lost some of his best troops when they defected to the naaru and draenei at Shattrath instead of capturing the city as he'd ordered.
Mastering naaru technologies proved difficult, however, as did his ever growing thirst for fel magics. Weaknesses that Kil'jaeden was quick to exploit in Kael'thas so Blizzard could have an excuse to use him as a raid boss. Entering into an alliance with the Burning Legion, Kael'thas intended to drain the remaining magic of the shattered world of Draenor, and then bring it back with him to Azeroth to feed his people using Tempest Keep. It was the perfect plan until a bunch of adventurers stormed his magic flying sky keep and killed him. Or so they believed. Not even moments later, Kael'thas mocked the foolish heroes for thinking he was actually dead, and swore revenge on them, the naaru, Illidan, and pretty much anyone else who was listening. Openly declaring his allegiance to his new master, Kil'jaeden, Kael'thas warned of his master's impending arrival and that all would be doomed.
"Don't look so smug! I know what you're thinking, but Tempest Keep was merely a set back."
So Kael'thas had a totally awesome plan to summon Kil'jaeden to Azeroth using the power of the reawakened Sunwell, and stole M'uru back from his own people in Silvermoon. Fel Blood Elves. Killed by agents of the Shattered Sun Offensive. The End.
Kael'thas, the Illidari in generally really, got a really raw deal in Burning Crusade. The reasons for us fighting them are tenuous at best, and Illidan and Kael'thas both got derailed largely to justify making them raid bosses. While Illidan's story arc was pretty much wrapped up in Frozen Throne, Kael'thas still had a lot of interesting stuff going for him before he got shoehorned into being crazy and evil. Did adventurers really kill him, or was he really killed by Blizzard first? You be the judge.