Cespenar is an imp who used to serve Bhaal as a "butler". He seems to have vanished out of existence along with that deity's death, but reappears when the player character in Baldur's Gate II: Throne of Bhaal arrives at the Pocket Plane they have unconsciously created to protect themselves within Bhaal's domain. Cespenar's function, aside from some comic relief, is to upgrade and create various enchanted items from the right ingredients – much like Cromwell, but with a longer list of possible items.
Cespenar likely ceases to exist again when the player character dissolves the Pocket Plane before the final encounter in the game.
Some of the items Cespenar can improve include: