Title: Rulers of the Darkness
Content:  Rulers of the Darkness (2002) is the fourth book in The Darkness Series by Harry Turtledove.
Title: Steven Spruill
Content: Rulers of Darkness (St. Martin's, 1998) ; Daughter of Darkness (St. Martin's, 1999) ; Lords of Light (Hodder & Stoughton Ltd., 1999) 
Title: Lords of Darkness
Content:  The second Lords of Darkness was released for the third edition of Dungeons & Dragons. The book was published in 2001, and was written by Jason Carl and Sean K. Reynolds. Cover art was by Mark Zug, with interior art by Adam Rex, Anthony Francisco, Matt Cavotta, Carl Critchlow, Michael Dubisch, Mike Dutton, Raven Mimura, Puddnhead, Stephanie Pui-Mun Law, Richard Sardinha, and Kalman Andrasofszky. The 192 page accessory details twenty-eight villainous groups, contains maps of evil strongholds, and includes new spells, feats, and magic items. The book presents five prestige classes: Darkmask, Entropist, Spur Lord, Thayan Knight, and Zhentarim Skymage. Monsters such as the Daemonfey appear in this book.
Title: The Law of Darkness
Content:  The Law of Darkness is a 1990 role-playing game adventure published by Mayfair Games for DC Heroes.
Title: Kings in Darkness
Content:  "Kings in Darkness" is a sword and sorcery short story by English writer Michael Moorcock. It was first published in Science Fantasy No. 54 in 1962. It has been reprinted as part of the Elric sagas and also reprinted in the anthology The Spell of Seven, edited by L. Sprague de Camp.
Title: The Law of Darkness
Content:  The Law of Darkness was written by Scott Paul Maykrantz, with a cover by Paris Cullins and Mike DeCarlo, and was published by Mayfair Games in 1990 as a 48-page book.
Title: War of Darkness
Content:  War of Darkness was written by Mark Perry, with a cover by Frank Frazetta, and was published by Mayfair Games in 1986 as a 32-page book and a removable cardstock map sheet.
Title: The Darkness Series
Content: Into the Darkness (1999) ; Darkness Descending (2000) ; Through the Darkness (2001) ; Rulers of the Darkness (2002) ; Jaws of Darkness (2003) ; Out of the Darkness (2004) 
Title: Darklords
Content:  RR1: Darklords is a 96-page Ravenloft accessory book published in 1991 for $10.95. It was written by Andria Hayday "with some additional design by William W. Connors, Bruce Nesmith, and James Lowder". The cover art featuring a "dagger-wielding lich" is by Tim Hildebrandt, while the interior artwork is by Stephen Fabian. David C. Sutherland III created the maps with 3D infrastructure views. In 2013, it was rereleased as a PDF on the DNDClassics website for $9.99.
Title: Lords of Darkness
Content:  main character or creature of each adventure and can be used to plan a series of encounters. "A Mundane Guide to Wards", by Greenwood (pages 85–91), explores the magic and lore of dealing with undead. "The Lords of Darkness", by Greenwood (pages 92–96), presents new spells for necromancers. Cover art for Lords of Darkness was done by Jeff Easley and interior art by Karl Waller, and the book was published by TSR in 1988 as a ninety-six page book. Editing was by Scott Martin Bowles, and cartography by Dave LaForce. This supplement was perfect bound, and released for the first edition of Advanced Dungeons & Dragons with product code TSR 9240.

Question: Who is the author of Rulers of the Darkness?
Answer: Harry Turtledove.
Dan Chernenko.
Eric G. Iverson.
Mark Gordian.
H.N. Turteltaub.
Harry Norman Turtledove.