Ed Greenwood
Ed Greenwood is a Canadian fantasy writer and librarian. He's most famous for creating the Forgotten Realms setting for D&D, which as of 5e is the default campaign world. He apparently sold the setting to TSR for a token fee in the 80s- which has got to sting now that toy-and-game goliath Hasbro are rinsing it for all it's worth, and other authors are churning out books in the setting that are way more popular than his own.
He's written a shit-tonne of books, often involving his self-insert not-Gandalf called Elminster.