Fundall the Forgetful
A Wizard who devised a spell to make an entire tree disappear. He just forgot he was sitting in it at the time. His sad demise offered a clue to Ponder Stibbons as to the underlying syntax of magical spells (used to program Hex as its equivalent of a computer language), as it was noted that Fundall's despairing scream of "Not THIS bit!" was not accepted by the syntax of his spell as a valid sub-set of "Make this tree disappear!"
This is evidently the equivalent of "Bad command or syntax" in spellcasting.
This occurs in The Science of Discworld.