Dimitri Vapnoople/Mad

Alternate Origin Theory
Although the most obvious theory of how Dr. Dim came to his present state is that the Baron felt the need (for science, along with other reasons of unknown merit) to neutralize his spark and left him substantially brain damaged (though not totally incapacitated—where on the spectrum of "getting much better" on the "quality of life issue" Dr. Dim falls is unknown) in the process, there is a potential alternative, when one considers that Dr. Dim is the most likely candidate for creator of the wasp weasel, which was originally designed to hunt slaver wasps, not just detect revenants. It is possible that (say, during the testing of what became the prototype) due to a lab accident, Dr. Dim himself was wasped. Supposedly, sparks ordinarily can't be turned into revenants. (Or can they? This wasn't such common knowledge that Theo excluded Klaus and the Mongfish from being wasped in his story.)

At any rate, there's reason to think that it's possible, at least, that if Klaus performed invasive brain surgery on Dr. Dim, it was not to destroy his spark but to study or eliminate a slaver wasp. Perhaps Dim himself, having been wasped, had such a great antipathy for the idea, that he volunteered to go under the knife to eliminate the wasp, and only secondarily try to learn why it was prevented from taking effect.