The worgen hail from a dark and treacherous world, from which there is no corner which is truly safe. There, the worgen battle their unflinching enemy in a vicious war; the Lords of the Emerald Flame. Ur, a mage of Dalaran, did research on worgen but never summoned them. Frustrated by the destruction of Dalaran by the Scourge and against the advice of his peers, Archmage Arugal elected to summon an army of the extra-dimensional entities by using Ur's research. The summoned worgen fought against the undead armies, but quickly turned on the wizards themselves. Driven mad with guilt, Arugal adopted the worgen as his children and retreated to the newly dubbed Shadowfang Keep, where he then cursed the village people of Pyrewood to turn into worgen whenever the sun went down.
Approximately at the same time, the night elf Sentinel Velinde Starsong was given the task to clear Felwood of demons. She prayed to Elune and was granted a magical Scythe which could summon worgen. She summoned larger numbers to fight at her side against the demons. Later Velinde began to notice that some of her force were unaccounted for. It was as though the Scythe of Elune no longer required her intervention for the summoning process. So she ordered them to remain at the Shrine of Mel'Thandris in Ashenvale and began to search for Archmage Arugal, whom she had heard also summoned worgen. From that point her fate was unknown, but it was rumored that she was killed in Duskwood and lost the Scythe. Black Riders from Deadwind Pass came to Duskwood looking for the Scythe and murdered a family of farmers in the search to find it. It is also known that the dark mage Morganth was searching for the Scythe of Elune, and stole Ur's Treatise on Shadow Magic as well.
In World of Warcraft: Wrath of the Lich King, Arthas has discovered Arugal's activities and has brought him back from the dead to work for him. This also means that there are a lot of Worgen allied with the Scourge in Northrend and in particular, the Grizzly Hills.