Originally posted by Sol Valentine
How was Arthas able to do that?
Trough manipulation from the spirit of the Lich King. The Lich King made sure trough strategical and intellectual maneuvers that Arthas Menethil picked up his enchanted runeblade. The runeblade secretivly 'sold' Arthas soul to the Lich King.
It did not take long until Arthas murdered friends, allied and family out of greed and thirst for power and set course to Northrend and the Icecrown glacier.
After an epic hunt and a just as epic battle between Illidan and Arthas, Arthas was victorious and climed Icecrown (Massive frozen throne where the spirit of the Lich King was located)
With the same runeblade that he found (Thanks to Lich King) did he scatter a frozen cascade that had imprisoned Lich King's spirit. As Arthas picked up the enchanted helmet, Arthas and Lich King's spirit fused into one powerful being.
Thereafter the Lich King was officialy born.