Abithrax was a red dragon on the island of Morgaath. Together with the other dragons allied with the Wyrmlords, Abithrax helped almost conquer the island until being defeated during the climax of Shadow of the Black Claw.
After licking his wounds, Abithrax followed the victorious adventurers to the main continent & helped the High Marches during the Greenwood Rebellion. Abithrax caused waves of destruction to the Greenwood & the Wood Elves who called it home. To put an end to that, the heroes of the Rebellion gathered and eventually slew Abithrax in his lair in the Lumin Desert.