Captain Callas was a human Starfleet officer who served as commanding officer of the USS Potemkin in 2267. That year, he relieved the USS Enterprise at Parathu'ul. (TOS novel: The Disinherited)

USS Potemkin personnel
USS Potemkin (NCC-1657)	J. Armstrong • D. Bailey • T. Barrows • Callas • M. Cleary • D.M. Flinn • J. Gaynor • Gladstone • Jonesy • L. Kelso • Konstantin • R. Lonergan • D. Paris • H. Takeshewada • Tutakai • N. Uhura
USS Potemkin (NCC-18253)	W.T. Riker