JRR Tolkien's non-fiction essay "On Fairy Stories" talked about "sub-creation" and the skills needed to create a "Secondary World" with an "Inner Consistency of Reality". I've chosen 7 authors for this list, and their "sub-creations". Each has been successful in a different way; all have other works outside the ones listed here. The authors and their worlds are as follows:
Stephen R. Donaldson -- The Land
Michael Flynn -- Firestar
Robert Jordan -- The Wheel of Time
CS Lewis -- Narnia
Anne McCaffrey -- Pern
JRR Tolkien -- Middle-Earth
Gene Wolfe -- The New Sun