Ancalagon The Black. Eärendil, on his ship Vingilot, slew Ancalagon with the aid of Thorondor and his Eagles. They fought Ancalagon for a whole day before Eärendil emerged victorious, and threw Ancalagon down upon Thangorodrim.
Speaking of Ungoliant, this impressive rendition by rubendevela on DeviantArt illustrates the showdown between Ungoliant and Melkor. I apologize in advance if I’ve given you nightmare fodder for tonight!