A very major character in Warcraft lore, to put an extremely long story short, his mom fought Ultra-Satan, defeated him, except Ultra-Satan put apiece of himself in her while she was pregnant with her child (Medivh), he was born and was basically next to be an Mega Baller named the Guardian of Tirisfal, later he becomes Guardian but Ultra-Satan starts to mess with him and then possesses him, which leads to the Dark Portal which leads to orcs and Medivh being murdered by a motley crew of Alliance guys but its too later.
Two sequels later he's brought back from the dead and is a prophet who seeks to stop Ultra-Satan coming back.
He brought up Medivh because in Warcraft 3 Medivh was very fond of turning into a Crow and back again, and it's even his "mount" in Heroes of the Storm.
He has a big Crow motif to him.