Mithrandir was a Drow Beguiler originally hired to locate the body or remains of Rayyn and report the outcome back to Rayyn’s noble family in the Underdark. However, after traveling to Tethyamar, Mithrandir quickly became entangled in the plotline and was the first party member to wield the Sting of Tenebrous after it had been given to him by the The Apothecary. Darian Skullbasher took possession of the Sting of Tenebrous after Mithrandir’s death.
Mithrandir was slain by a Mountain Troll when the party engaged in a side quest to slay some trolls and retrieve their hides for Zeke the Halfling.
UPDATE: Once the Party learned that they were clones, they realized shortly thereafter that the Mithrandir who died at the hands of the Mountain Troll was also a clone. The original is still alive and with the original party members…