I have several.
Robert Louis Stevenson -- Author of
Treasure Island. I read this book a long time ago, and back then I admired his writing so much I tried to emulate how he constructed his works.
A.E. van Vogt -- Author of
Slan,
The World of Null A, and co-author of
Slan Hunter. I read all these books, and I simply love reading his action-packed way of doing things. One of his contemporaries referred to his style as "One-Damn-Thing-After-Another," and it's that style that keeps me turning the pages of his books.
J. Michael Straczynski -- Creator of
Babylon 5, one of my all-time favorite SF television programs. His sense of reality, of incorporating ordinary, every-day people into a futuristic world of alien technologies -- characters I can identify with -- has made at least
B5 (I can't speak for any of his other stuff; I've not seen or read it) one of the most realistic series I've ever watched ... and one of the most interesting.
Jane Yolen -- Author of
Dragon's Blood,
Heart's Blood, and
A Sending Of Dragons. This author's vivid portrayal of an arid world called Austar IV, and its rough-and-tumble society, combined with loads of surprises and plot twists, was really one of the main reasons I started getting into works that incorporated dragons. In fact, one of the scenes in
Dragon's Blood gave rise to my first short story dealing with a character in my old PA novel, and the world in which he lived, lives on in my mind, constantly vying for attention in my quickly-rejuvenating imagination.
Anne McCaffrey -- Author of
The Dragonriders of Pern series, and
The Harper Hall of Pern series. These early books of the planet Pern, along with some of her older short stories, have inspired me immensely in my own writing. Like Stevenson, van Vogt, Straczynski, and Yolen, Anne McCaffrey shaped a lot of how I viewed story-telling and how it should be done. Having read her Pern books up to
Dragonsdawn, I have found a bright world filled with believable characters and, though there was a presence of an all-powerful evil (the Red Star, and the resulting Thread that constantly threatened their society) there was really no sense of Good Versus Evil among the characters. This impresses me, even to this day. I've always valued interesting and/or realistic characters, and hers are most certainly both.
So these are the several authors I really admire more than just about any others. I'm sure, if I gave more thought to the subject, I could probably come up with a couple -- if not a few -- more that are worthy, in my own opinion, of mention here. But for right now, the five I've already listed are plenty.