Philbert Olio (or possibly Oleo) is the (In)famous (and unctuous?) author of "The Heterodyne Boys and the Pneumatic Oyster", of which we have heard Agatha read one scene wherein Klaus winds up in a tar vat and discusses ✣ it with Punch.
Possibly the same person as Phil Foglio, who is sometimes referred to as Philbert — that is where "Philbert" on this wiki redirects to. Could also be a fraud, trying to cash in with a similar sounding name and material as the other author, and hoping the Baron's wrath would be shared with him?
Possibly relevant outside information[]
"Philbert" sounds like "filbert", which is another name for hazelnut, and "oleo" is another name for margarine, or butter substitute. Hence, hazelnut butter.