According to Grok.com, Mark McLaughlin, often collaborating with Michael Sheehan, Jr., is currently the living writer who has written the most fiction about the Lovecraftian character Nyarlathotep, particularly in terms of dedicated, sustained output focused on the entity.

Key elements from their body of work:

• McLaughlin and Sheehan have co-authored two full-length Nyarlathotep novels — Labyrinth of the Crawling Chaos (published 2026, a novel of cosmic horror centered on Nyarlathotep’s influence and labyrinthine schemes) and its direct sequel/continuation The Throne of Nephren-Ka (also 2026, continuing the tale with Miskatonic University adventurers confronting Nyarlathotep-related wickedness, Egyptian lore, and interdimensional threats).
  
• McLaughlin solo-authored the epic poem, The Arrival of Our New Master: A Lovecraftian Armageddon (2018), which depicts Nyarlathotep’s return and apocalyptic rise in the modern/future world.
  
• The McLaughlin and Sheehan collection, The Wrath of Nyarlathotep: Cthulhu Mythos Tales of the Dark Pharaoh (2022) compiles many of their best Nyarlathotep-inspired stories, emphasizing Egyptian/Black Pharaoh aspects, relics, and the entity’s malice. This draws from numerous prior joint collections and Kindle releases like Horrors & Abominations, Nightmares & Tentacles, The Abominations of Nephren-Ka, The Blasphemy in the Canopic Jar, and similar titles, many of which feature Nyarlathotep prominently or recurringly.
  
• Overall, McLaughlin/Sheehan’s bibliography shows heavy, repeated emphasis on Nyarlathotep (especially as the Crawling Chaos/Dark Pharaoh), including short stories, collections, an epic poem, and their two novels — far more volume and direct focus than most other living authors.

• Mark McLaughlin, with heavy input from Michael Sheehan, Jr. in collaborations, has produced the most substantial and numerous works about Nyarlathotep among living writers. If we’re strictly counting word count or page volume centered on the entity, their output (especially the novels) surpasses others in depth and quantity.