The group that would eventually come to be known as the Eyes of Hadar originally gathered to do a job for Lord Markelhey of Fallcrest. They retrieved an heirloom chalice for him from some ruins in Talon Pass.
After their success in working together, they decided to take a job tracking down some slavers who had apparently disappeared into the labyrinth under Thunderspire Mountain. A hunter from Harkenwold hired them on behalf of his baron to return some locals who had been taken as slaves.
Once in the mountain, the group (consisting of Hadarai the warlock, Gadrik the rogue, and Ingar the ranger) Quickly made the acquaintance of the halflings of Halfmoon House (by saving Rendil Halfmoon from slavers).
With the help of Rendil and the Drow trader Gendar, the trio managed to track down most of the enslaved villagers; along the way dispersing the Bloodreaver slaver gang and taking their hideout, assaulting the local stronghold of the Grimmherzhul Duergar three times, and fighting a war of attrition with the Blackfang Gnolls (which almost cost them their lives on a couple of occasions and resulted in a few of the slaves they were trying to rescue getting sacrificed to Yeenoghu).
They discovered that the Bloodreavers and the Blackfang Gnolls were both working for a renegade wizard named Paldemar, who was nominally a member of the cohort of mages who ruled the Seven Pillared Hall (The Mages of Saruun). They tracked Paldemar down to his hideout in the Tower of Mysteries and disrupted his plans to take over the entire labyrinth. They were forced to retreat before the mage’s forces though, and the Mages of Saruun rewarded them handsomely and took over the pursuit of the rogue wizard.