Pedantry - KSM

Medivh, the final Guadian of Tirisfal (Med'an is non canon, shut up), was corrupted before his birth by Sargeras. When Aegwynn defeated the Avatar of Sargeras in Northrend, a fragment of the latter's soul transferred itself into her pregnant body, latching onto Medivh's unborn soul. This event would shape Medivh's entire life, leading to the death of his father, a decade long coma, the annihilation of an entire troll army, and the opening of the Dark Portal to Draenor.