Geshthax had graying, rusty scales and long tasseled plumes. He had lost his right arm.
When he was young, he was kidnapped by followers of Tiamat who wanted to ransom him in exchange of the Breath of Petron. When Clan Shestandeliath refused to give in the artifact, the cultists severed his right arm as a punishment. He was later rescued by a detachment of Lance Defenders.
During the invasion of Tymanther of 1479 DR, Vanquisher Kepeshkmolik Tarhun asked Clan Shestandeliath to use the Breath of Petron to deal with the invaders, Geshthax refused to follow the order for personal reasons. Many believed this was because Geshthax was either a coward or wanted to kill Tiamat's followers with his own hands.
On Hammer 9 of 1487 DR, Geshthax sacrificed himself in order to active the Breath of Petron so he could raise an earth barrier to surround Djerad Thymar and protect the city against Gilgeam's forces. Although Geshthax didn't died by using the artifact, he was left impaired and his daughter, Shestandeliath Narhanna, succeeded him as the new matriarch of Clan Shestandeliath.