Rose Estes
Rose Estes is blamed, alongside Lorraine Williams and Carl F. Sargent, for destroying the Greyhawk setting for a decade.
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.