Timothy Zahn is a science fiction writer best known for his work with Star Wars, and by "best known," we mean if you were to call Zahn the Dan Abnett of Star Wars, you wouldn't be far off. Zahn's books were the first to (semi) officially continue the story of the main characters where Return of the Jedi left off, and are pretty much what kick-started the old Star Wars Expanded Universe, laying the groundwork for the hive city-sized mountain of supplemental material it would grow into, and Zahn's stories and characters are still considered the best things in it. Seriously, the loss and overwriting of Zahn's material in particular is probably one of the biggest issues Star Wars lorefags have with the new trilogy and the axing of the Expanded Universe as a whole.
Thankfully Disney seems to have figured this out and have brought one of Zahn's greatest characters, Grand Admiral Thrawn, back into the canon via Star Wars Rebels, and Zahn himself has been commissioned to write a new Thrawn novel (with a sequel confirmed!).