Milil was at one time the minor deity of song, before getting cast out of Faerûn's pantheon by Cyric. Withers pulled him from the Fugue Plane in order to "honour the worthy" with his songs.
The player character may pass a passive Religioncheck during conversation to recognize him, greatly improving his spirits. Alternatively, the player character can pretend to recognize him by passing a DC 18 Deceptioncheck.
He functions as a jukebox for the Epilogue celebration; talking to him allows you to change the song that is playing.