Wilderlands Age of Worms
Ancient Orichalan Dragon Lord
Icosiol was one of the Wind Dukes, a particularly important group among the Dragon Lords of Ancient Oricha. According to the Chronicle of Chan, the Wind Dukes were responsible for halting and turning back an invasion (masterminded by Demogorgon) of the Ghinor Highlands by forces from the Demon Empires to the south. Icosiol was the leader of the Wind Dukes, slain at the Battle of Night’s Dawning. The party discovered his glyph on a strange, shattered arcane apparatus in the entry hall of the Whispering Cairn.
You can be sure the name Icosiol is going to come up again. Otherwise, why would he be in the NPCs list, right?
The party would, much later, enter his tomb to rescue Master Penkawr and retrieve some important treasures.