Mehlar Dawnblade is a Blood Elven Blood Knight and an ex-member of the Knights of the Silver Hand.
Mehlar served in the Alliance troops as a Paladin during the Second War. His valorous actions eventually earned him a place amongst the Knights of a Silver Hand, and he was further mentored in his path by the renowned Uther Lightbringer himself. Nevertheless, when the Third War ended to Arthas's betrayal, Uther's death and the corruption of the Sunwell, Mehlar renounced his Paladinhood, vowing never again to serve the Light that had forsaken his whole kin. He had apparently been suspicious of Arthas from the beginning and also had tried to warn Uther, but Uther had not heeded his warnings. This left Mehlar permanently bitter, and he has been rather openly declaring his anger and hatred towards both Arthas and Uther.
Mehlar's parents were killed during the Third War while fighting against the Scourge. He has a younger brother, Aenor, but their ties were mostly severed after the war when Mehlar discovered that Aenor didn't participate in the defense of Quel'thalas, causing him to think that Aenor thus was partly responsible for the their parents's deaths.
After renouncing his Paladinhood, Mehlar soon joined the Blood Knight Order and quickly advanced in their ranks. He is currently stationed at the Bulwark in Tirisfal Glades, near the border of Western Plaguelands. Sometimes, promising newer members of the order are sent to him for a task where they can test their skills against greater foes.
Mehlar is a real NPC from the game, but while some parts of his background (such as the fact that Uther was his mentor and his hatred towards him) have been indeed deduced from his speech, others are purely products of imagination made for the convenience of a storyline.