Robur Heterodyne is an ancestor of Agatha's, whom Castle Heterodyne describes as "refreshingly simple". (The Castle is the of the following information, along with a found in the Hermitorium of Van Rijn in the Immortal Library under Paris.) Robur claimed his place in the family history with his experiments which investigated the nature of and/or meddled with the very fabric of Time. These probings inadvertently attracted the personal attention of (a trio of?) certain hideous extra-dimensional terrors a.k.a the Dreen. Considering what these entities are of, it is understandable that Robur concluded that they were "angels" sent to punish him for some sinful transgression (though, true to family form, he wasn't quite sure which). He experienced a genuine crisis of faith from their presence, and smashed the device(s) that brought this revelation forth. This did not dismiss the Dreen (although Castle Heterodyne seems to believe it did), and in desperation Robur turned to those expert monster-corrallers the Corbettite Monks, who agreed to haul away the (surviving?) device that was causing the problem, taking the Dreen with them. In exchange, Robur pledged to stay out of Corbittite territory (a promise he atypically kept) and then had some pie, crisis overcome.
"Robur" is Latin for "oak". It is also the name of the main character in Jules Verne's 1886 novel "Robur the Conqueror" (also known as "Clipper of the Clouds") and its sequel "Master of the World".