Question: Sagas of the Demonspawn is a four issue gamebook series written by J. H. Brennan, and who illustrated the latter two, by which British fantasy and science fiction illustrator and modeler known for his work for Games Workshop's White Dwarf magazine, Warhammer Fantasy Battle, Warhammer Fantasy Roleplay and Warhammer 40,000 games?

Context paragraphs:
John Blanche: John Blanche is a British fantasy and science fiction illustrator and modeler known for his work for Games Workshop's White Dwarf magazine, Warhammer Fantasy Battle, Warhammer Fantasy Roleplay and Warhammer 40,000 games and his role as art director for the company, including his work in the field of fantasy miniature painting, and for illustrations for various game book and Fighting Fantasy publications.

Chaos (Warhammer): In Games Workshop's "Warhammer Fantasy" and "Warhammer 40,000" fictional universes, Chaos refers to the malevolent entities which live in a different timespace, known as the Warp in "Warhammer 40,000" and as the Realm of Chaos in "Warhammer Fantasy".  The term can refer to these warp entities and their influence, the servants and worshippers of these entities, or even the parallel universe in which these entities are supposed to reside.  The most powerful of these warp entities are those known as the Chaos Gods, also sometimes referred to as the Dark Gods, Ruinous Powers, or the Powers of Chaos.  Similarities exist between the Warhammer idea of Chaos and the concept of Chaos from Michael Moorcock's Elric saga, which also influenced D&D's alignment system.  Further similarities can be seen with the godlike extradimensional Great Old Ones of horror writer H. P. Lovecraft's stories.

Warhammer 40,000 Apocalypse: Warhammer 40,000 Apocalypse is an expansion to the Warhammer 40,000 tabletop miniatures wargame by the British gaming company Games Workshop.  It contains rules which allow players to field massive armies the likes of which are unwieldy using the basic Warhammer 40,000 ruleset.  It also allows players to field units that are not available in normal Warhammer 40,000 games, such as large super-heavy tanks and robot-like titans, some of which are almost a foot tall.

Realm of Chaos (Warhammer): The first version of Realm of Chaos is a two-volume publication by Games Workshop concerning the forces of Chaos.  The hardback books contain background material and rules for "Warhammer Fantasy Roleplay" (1st edition), "Warhammer 40,000: Rogue Trader" and "Warhammer Fantasy Battle" (3rd edition).

Warhammer Fantasy Roleplay: Warhammer Fantasy Roleplay or Warhammer Fantasy Role-Play (abbreviated to WFRP or WHFRP) is a role-playing game set in the "Warhammer Fantasy" setting.  Over the years, it has been through a number of phases and different publishers, most of which were related in some way to Games Workshop.

Warhammer 40,000: Warhammer 40,000 (informally known as Warhammer 40K, WH40K or simply 40K) is a tabletop miniature wargame produced by Games Workshop, set in a dystopian science fantasy universe.  "Warhammer 40,000" was created by Rick Priestley in 1987 as the futuristic companion to "Warhammer Fantasy Battle", sharing many game mechanics.  Expansions for "Warhammer 40,000" are released periodically which give rules for urban, planetary siege and large-scale combat.  The game is in its eighth edition, which was released on June 17, 2017.

Armies of Warhammer: Armies of Warhammer are components of the table-top games Warhammer Fantasy Battle and Warhammer 40,000.  The armies have been defined into a separate "army list," and they are described in more detail in the Warhammer Army Book or Warhammer 40,000 Codex.  Players of either game, or their spin-offs, have a wide variety of army choices and each army can be customized to suit a particular playing style.  All games are produced by Games Workshop.

Games Workshop: Games Workshop Group PLC (often abbreviated as GW) is a British miniature wargaming manufacturing company.  Games Workshop is best known as developer and publisher of the tabletop wargames "Warhammer Age of Sigmar" (previously "Warhammer Fantasy Battle"), "Warhammer 40,000" and "The Lord of the Rings Strategy Battle Game".  The company is listed on the London Stock Exchange with the symbol GAW.L.  The company's British operating subsidiary company is Games Workshop Limited.

Sagas of the Demonspawn: Sagas of the Demonspawn is a four issue gamebook series written by J. H. Brennan and illustrated by Geoff Taylor (first two books) and John Blanche (latter two).

Warhammer Fantasy (setting): Warhammer Fantasy is a high fantasy fictional universe created by Games Workshop and used in many of its games, including the table top wargame "Warhammer Fantasy Battle", the "Warhammer Fantasy Roleplay" (WFRP) pen-and-paper role-playing game, and the MMORPG "".

Supporting paragraphs: Sagas of the Demonspawn John Blanche
Answer: John Blanche