These kinds of threads seem to be popular right now, so I'll take the opportunity to make the most obvious one.
Varian is a strong leader and he has his heart in the right place. He was possessed by the wolf ancient Lo'gosh, but he learned to control his rage. A weaker person would've succumbed to the bloodlust of the ancient. Varian has suffered a lot in his life and most of what he had to endure was because of the orcs. When he was young his father was killed cowardly by Garona, an orc that served as an ambassador between Stormwind and the orcish Horde, but turned on the king, who trusted her. Anduin Lothar, the lion of Azeroth and a friend to his murdered father, was killed on the battlefield by Doomhammer. His friend Arthas, son of King Terenas, who had taken care of him after his father's death, turned on his own people and became the Lich King. Years of battling between the orcs and the humans have brought forth misery and death among his own people, yet he doesn't strafe from his goal. His wife was killed during riots by the Defias, leaving him with his son, the only thing he has left in his life. He was captured by Onyxia and split into two. One half was eventually enslaved by an orc, who forced him to fight as a gladiator. One of the places where he had to fight was Orgrimmar, right under the nose of Thrall. In his absence his son ruled over his people, and Bolvar Fordragon, who was "killed" later by the partnership of the Horde, watched over little Anduin in Varian's absence.
Varian has lost a lot. He has lost a lot of people, who were close to him and he had to fight all his life - against the orcs, for his own freedom and even against his own temper. Still he fights on, to drive those, who threaten the peace of his people, from this world.