Drasek Riven

Drasek Riven is a one-eyed former Zhentarim assassin, former rival, and now friend of Erevis Cale.

Background
After he and Erevis were pulled into a near-death experience at the hands of a shadow adept named Vraggen and his slaadi partners, they grudgingly joined forces to oppose them. During this period, Riven and Cale became the first and second of Mask's five mortal servants and are sometimes known as the right and left hands of Mask.

Riven is Mask's Second, following Erevis Cale as his friend and associate. As Mask's second of five, Riven was imbued with certain skills reminiscent of a divine champion, including a shadow-based lay on hands, and divine wrath which causes his sabers to bleed

shadow. He was also given the Black Speech which, when spoken, causes anyone within earshot to experience nausea and pain.

Riven is a devout follower of the Shadowlord, and the caretaker of his temple which was stolen from the mad god Cyric. This temple was magically moved by a Githzerai sorcerer named Vhostym to the Wayrock where it still stands.

Riven is a cold-hearted and efficient killer, and has never shown any soft spot towards anyone or anything other than canines and children. Riven's eye was lost in a beating he received from an Amnian nobleman who was the slave master of him and his mother when he was a child. Riven was a kennelboy at the time, which is how he acquired his affinity for dogs. He became an exarch when he inherited part of Mask's divine essence after the battle with Kesson Rel.

Recent Activity
After the events of the Shadowstorm and Kesson Rel's destruction, Riven realized Mask might have been onto something. After the Spellplague, Riven found that Varra was carrying Cale's son and that Mask had hidden her somehow. He has been tirelessly searching for Varra and has no intention of stopping until he has found her and her son. Riven also knows that the Shadovar also look for the boy and that twarting the Shadovar entirely would buy him time. To accomplish this, Riven had brought a group of adventurers together so that they might bring about a catalyst that would mark the fall of the Netherese.

References:

Forgotten Realms Wikia

The Erevis Cale Trilogy by Paul S. Kemp

The Twilight War by Paul S. Kemp