Much of Gamalon's family, including his mother and two oldest siblings, were killed in 1313 DR, when Gamalon was only eleven-years-old, during a series of feuds that occurred between his family and Clan Trecask from the Duchy of Dusk.[8]
Gamalon was educated at the Mystics' Academy in Erlkazar.
Sometime in his early life, Gamalon became an adventurer and explorer.[6] During one of these early adventures, Gamalon lost his left eye to an owlbear. At some unknown point, he received his magical gem eye as a gift from Khelben Arunsun.
In 1333 DR, Gamalon left Toril and his homeland of Tethyr and lived on the Rock of Bral, one of the Tears of Selûne, where he maintained a curio shop. At some point while there, Gamalon discovered a secret stash of orbus rings, which enhanced the power of spelljamming helmsmen. For a time, Gamalon was the only seller of such rings.
During his time on the Rock of Bral, he became enamored with a merchant's daughter, named Mynda. After four years of pursuing her, she finally agreed to become his wife.
During the Ten Black Days of Eleint, one of his sisters and one of his brothers and most of the members of their families were slain for being nobility.
Gamalon returned to Toril, to his grandfather's lands in County Spellshire near the Forest of Tethir, sometime before the First Siege of Myratma. He provided magical support in both the First and Second Sieges, and for this, he was rewarded his grandfather's old lands to rule over as count.
In 1370 DR, Gamalon, his daughter, her husband, and Timoth Eyesbright traveled to Trailstone after that town defected from Amn. These four helped train the citizens in defending their city.
In 1374 DR, Gamalon planned to break the "Tethyr Curse" by staying in Waterdeep over the winter. He planned to give guest lectures at Blackstaff Tower. On Uktar 28, 1374 DR, Gamalon, together with his wife and his party, arrived back at the Sleeping Dragon inn, on their way back to Waterdeep after a trip to Longsaddle. Raegar Stoneblade and Damlath had brought the Diamondblade to the inn, and Gamalon's green gem eye caused lightning bolts to transmit between it and the blade, destroying the front of the building and a large area of the upper floor.
Gamalon Idogyr, Raegar, and Damlath survived, but Gamalon's wife, many guards, and other bystanders were killed in the incident. While Gamalon was laid low, Damlath (who was possessed by the lich Priamon "Frostrune" Rakesk) stole his gem eye.
Gamalon joined in Khelben's plan to stop Priamon, and the lich was defeated. At the end of the ordeal, Mystra herself rewarded him by giving him a new magical left eye.