Since most of you already know lots about lich king, I will tell Sonya's feats in diablo 3
Sonya is basically a one man army capable of slaughtering entire legions of demons with ease
Managed to liberate 3 entire continents single handedly
Defeated the Embodiment of evil itself Diablo singlehandedly (which is a spawn of Tathamet, which again is somewhere around Sargeras level).
Killed Death himself, Malthael Singlehandedly