Malikith

During the siege of Rivgraad in 436 YoU by the drow Bloddwyn Bluainach, Bran Sparkhammer and Alvery Vestergaard together with their companions witnessed an arguement between a cloaked human and a Yochlol. The fiend was demanding more support from the master of the man she called 'Malikith' and threatened him. He quickly put the powerful demon into her place and pointed out that the demons were where they were summoned by the drows and its not his problem that the drow were failing.
When guards around them noticed the approaching party of the city's defenders the Yochlol attacked while he disappeared.
Based on what demons the city fought the party assumed that Malikith must be an agent of Ka'ash'Du'Maal'Barid.

In 438 YoU in Rykthaven a letter was found on some cultist serving the Nameless One that indicated Malikith's involvment in events around the continent implicating a green hag called Pyrna to be working for him.