Kodarek the Dread

Kodarek the Dread was the leader of the Dragon Army of Tiamat.
No one really knows where this Githyanki came from, but it was from another plane of existence. He arrived shortly after the first Great Dragon War, where the chromatic and metallic dragons had gone to war. Soon after, the humanoids of the realms soon followed suit. This eventually led to the fall of Draigenmore in 252 AD as the kingdoms split apart.
There was an order, called the Sons of the Dragon —an order that served dragons as deities--that believed if they could broker peace once again among the dragons, then such peace would follow among the humans and other races as well. This was destined for failure.
But there was another incident that led to the fall of the Sons of the Dragon as they once were….a being named Kodarek the Dread came from another plane, claiming to be a direct servant of Tiamat, Queen of the Dragons, herself. He quickly took control over the Sons of the Dragon and over 1000 years he perverted the organization into what eventually became the Dragon Army of Tiamat  that attempted to bring her back into our realms in the Second Great Dragon War in 1348-1350AD.
As he took the Sons of the Dragon  north into Sundra, Kodarek also gave shelter to a mass exodus of Drow who were being driven from the lands of Draigenmore.  He also enslaved the Ice Dwarves of Sundra with his power.  It was here, at the Northern most tip of the world, that Kodarek had his followers build the Dragon Temple.
He brought others into his inner circle, sharing rule of the Dragon Army with Llolth Queen of Spiders, and Betewl the Beholder.
Kodarek failed to bring Tiamat back into the realms, and was killed by The Dragon Watch thus ending the Second Great Dragon War.
Some of his followers still believe his exists...somewhere.