Despite his promising beginnings, Arthas became one of the most powerful and evil beings Azeroth would ever know. Taking up the cursed runeblade Frostmourne, he became a death knight, led the Scourge in destroying Lordaeron, and merged with the Lich King. Ruling as the dominant personality of the Lich King for years afterwards, Arthas was defeated in combat by adventurers of the Alliance and the Horde. Cradled by the spirit of his father, King Terenas, Arthas Menethil died, leaving the mantle of the Lich King to be taken by a noble soul who would contain the power of the Scourge.
It was during this time that Arthas met the youngest daughter of Daelin Proudmoore, the sorceress Jaina. Over the years, they grew close as friends, and then romantically. They were very much in love with one another. But, eventually Arthas would question whether the two of them were ready to be together. Arthas would abruptly end the relationship so Jaina could focus on her magical studies in Dalaran and Arthas could focus on his commitments to Lordaeron. Shortly after, they would agree to rekindle their romance, but this was during the beginning of the Scourge invasion that would change both of their lives forever.