Nalzmyr

Nalzmyr is a half-drow warlock and member of the Savage Seven. He fights with a falchion etched with shadowy eldritch runes that he summons forth with magic. He is also an expert survivalist, having been raised on the run in the underdark. His father was a bedine nomad, and his mother a drow priestess of lolth. His father left with him the Svirfneblin of Blingdenstone the last time he saw him (leaving the falchion behind).
While in silverymoon, he discovered a dead warlock follower of the lord of shade (his patron's enemy). He revealed this information to the party, and the fact that he communes with his patron (who resides within his sword) and receives visions from him.
With Keladrien's research, he learned much about what the enemy warlock was researching in Silverymoon (about the Netherese Empire and the Phaerimm).
In the underdark beneath Sundabar, Nalzmyr's patron finally manifested himself as the party battled Phaerimm. He revealed himself to be Melegaunt Tanthul, one of the princes of shade. He also revealed how he had come to exist within the sword "souleater" and that his hated enemy was none other than the former adventurer Firble Gemcutter. Melegaunt then pointed the group towards the city of Chaulssin within the underdark.
When the Savage Seven died in the underdark, their mission to stop Firble failed. He captured and absorbed Melegaunt's brothers and became the new Lord of Shade. Firble traveled to the material plane atop the reborn shade enclave of Gloomwrought and attacked Sundabar, where he was repelled by the alliance of the silver marches, though the heroes that entered Gloomwrought to kill him perished and the city fell atop Sundabar, utterly destroying it.
Melegaunt is the last of the princes of shade, and he warns that Firble is defeated but remains trapped in the shadowfell for now. He continues to travel with Nalzmyr inside the blade souleater, unable to take form outside of the shadowfell (or near the planar rifts in the underdark).
During his travels in the Thaycreep, Nalzmyr visited the shadowfell and discovered Firble imprisoned by the raven queen and quite mad. He delivered the killing blow to his most hated enemy, releasing the shade princes and allowing them to begin to retake the shadowfell from the raven queen. He later died battling a death tyrant in the search for Szass Tam's phylacteries and was raised as a zombie (and subsequently destroyed by his Dorn).