Rose Estes
Rose Estes is blamed, alongside Lorraine Williams, for destroying the Greyhawk setting for a decade. Although there was blame to be shared, Skip Williams being a dark-horse candidate; and Carl Lynwood Sargent's attempts to fix it all should be scored with the theme to The Magician's Apprentice. But we are here to discuss Estes.
Estes started out June 1982 by kicking off the Endless Quest series of TSR-introducing choose-your-own-adventure books. These books were gold, if you were nine years old - and that's not an insult, because we were all nine once, and when we were old enough for our parents to buy full D&D (or Top Secret, Gamma World - whatever), Estes' books were often how we found out about those RPGs.
But then You Know Who figured Rose for a great choice to write full adult novels in the long-revered Greyhawk setting. To follow Gary Gygax Himself. Estes was... not up to this.
Eric Mona posted a widely-read rant, "The Shame of the Rose", on the full fail of these novels. Linking to an even wider-read rant. We don't believe poor Rosie ever recovered from these.
Estes is, it seems, an object lesson in the Peter Principle.