Nyarlathotep

Nyarlathotep was one of the Great Old Ones given its name in the present universe by Rassilon. (PDA: Divided Loyalties) He was considered the darkest and greatest of the Old Ones. Elektra, who despised Nyarlathotep most of all, hoped her child, Kronos, would be the champion of a united universe against him and his kind. (PDA: The Quantum Archangel) The Doctor told Bernice Summerfield that he sincerely hoped never to meet Nyarlathotep. (NA: All-Consuming Fire)

Behind the scenes
Nyarlathotep originated in the horror stories of H. P. Lovecraft, in which he is among the most powerful of the Great Old Ones.