Highlord Alexandros Mograine was the leader of the Four Horsemen in the Warcraft universe. He was a leader of the Knights of the Silver Hand but was later raised as death knight by Kel'Thuzad.
Alexandros witnessed an orc warlock channeling magic into a mysterious orb during the the Silver Hand's attack on Blackrock Spire. When he tried to claim it for his people, Alexandros' hand was badly mangled.
After the Scourge arrived on Lordaeron, Mograine revealed his discovery to his most trusted comrades within the Silver Hand. One of his comrades casted a holy spell on the crystal. The crystal absorbed the spell and became filled with pure light. Mograine placed his hand on the crystal which restored his hand to its former self. Shortly after witnessing this event, Mograine and his comrades named it the Ashbringer and asked Magni Bronzebeard to forge a blade for the crystal which he did.
However, Kel'Thuzad heard of the blade and arranged a deal with Balnazzar to corrupt Mograine's oldest son into killing him. Alexandros was killed by the Scourge's ambush and the Ashbringer was corrupted. Kel'Thuzad raised Alexandros into a death knight serving the Scourge and led the Four Horsemen.
Alexandros' other son Darion led a small team of Argent Dawn agents into Naxxramas to defeat his father and Kel'Thuzad. Highlord Mograine and the other horsemen killed the rest of group especially Grunn'Holde who the Higlord personally killed, leaving Darion the only survivor of the group. Darion killed Alexandros and took the Ashbringer with him and left his father behind. Alexandros' spirit confronted Renault and killed him without mercy.
During the Scourge's assault on the Light Hope's Chapel, Darion impaled himself with the Ashbringer. The armies of the Scourge were decimated and Alexandros was redeemed and freed.