Krull

Krull was Arkhan the Cruel's top advisor and the Cult of Tiamat's local mad scientist in Avernus. The insane tortle was a death cleric of the Dragon Queen who carved draconic symbols into his shell as a constant reminder of his devotion to himself and those around him. Following Arkhan's acquisition of the Hand of Vecna, Krull's chief duty was finding ways to alleviate its negative side effects. 
This work was primarily done in his lab on the third level of Arkhan's tower. Krull commonly made a salve that's main ingredients included crushed unicorn horn and the soul of a Good-aligned creature to keep the Hand of Vecna's necrotic rot at bay. Krull was frequently assisted with his experiments by a host of undead that also doubled as guards for the lower layers of the tower. Though they were composed of only common zombies and skeletons, Krull's experiments gave the undead hordes the ability to combine themselves into more powerful creatures.
When a group of adventurers hired by Lady Kemlar attacked Arkhan's Tower, Krull was their first target as battle broke out between them and Arkhan the Cruel's inner circle. However, Tiamat's worshippers were aware the adventurers were coming and Krull had the good sense to cast a regeneration spell on himself prior to their arrival to the tower's roof. This made the tortle extremely difficult to kill, though the adventurers did focus fire and slay him with an arrow before his wicked magic could do them much harm.

Circumstances of Death

Shot with an arrow by Ibrahim Moizoos' summoned celestial

Belief/Deity

Tiamat, Queen of Evil Dragons