Originally Posted by
Calfredd
I can prove you wrong.
The Lich King was originally an orc named Ner'zhul who was tricked by Kil'jaeden to turn the peaceful, shamanistic orcs into bloodthirsty warriors and warlocks. When everything went down the crapper, Ner'zhul opened a bunch of portals but was caught by Kil'jaeden. His spirit torn from it's body and tortured, Kil'jaeden gave him one last job to redeem himself and was fused to a special set of armor and was jettisoned to Azeroth in a chuck of ice from the Twisting Nether.
Arthas was a paladin for the Silver Hand and son to the king Terenas and was sent out to deal with the undead in Stratholme. Arthas gave the order to purge the city and met Mal'ganas who goaded him to go to Northrend. After Arthas found Frostmourne (planted there by Ner'zhul) he became Ner'zhul's puppet and started killing his own men and, when he came home, his own father as well.
After Illidan set off to kill Ner'zhul, Arthas was called to Northrend to defend him. Arthas won the altercation with Illidan and ascended the climb to the Frozen Throne where, using Frostmourne to break the ice, donned the armor and helmet where Ner'zhul could completely take over Arthas. This failed resulting in Arthas have complete control and when we finally fight him, it's 100% Arthas. We (Tirion) shatter Frostmourne and kill Arthas once and for all. The Frost-spec Death Knights gather the shards of Frostmourne to make new weapons so there's no sword to take back. Sylvanas also saw Arthas' spirit in the same purgatory and her spirit when she killed herself after accomplishing her life mission of revenge on Arthas.
Left out a lot of detail but to make things short:
Arthas=Human
Lich King= Orc spirit named Ner'zhul
Frostmourne= New Death Knight player weapon
Ah but I did leave out that Ner'zhul created the plague that causes undeath to create an undead army to weaken Azeroth's inhabitants so that the Burning Legion would have an easier time invading.