Prince Arthas Menethil was born to King Terenas Menethil II, four years before the start of the First War. The young prince grew up in a time when the lands of Azeroth were ravaged by war, the Alliance was crumbling, and darker clouds still loomed on the horizon. As a young child, he became friends with Varian Wrynn.
As a youth, Arthas was trained in combat by Muradin Bronzebeard, the brother of the dwarven king Magni Bronzebeard, and became an adept swordsman. Under the tutelage of Uther the Lightbringer, Arthas was inducted into the Knights of the Silver Hand at the young age of 19. The ceremony was held in the Cathedral of Light in Stormwind City, and it was then that Arthas was given the holy mace called Light's Vengeance.
Despite his rash and headstrong behavior, Arthas became a renowned warrior. One of his more famed exploits was counterattacking a group of forest trolls striking at Quel'Thalas from Zul'Aman.
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.