- "—And now the Curators seem to think we’re the new Heterodyne Boys!"
Aldin Hoffmann is a relatively minor functionary in the Immortal Library of the Great Architect in the catacombs under Paris. He is the brother of Jiminez Hoffmann. Aldin was at first referred to exclusively by his first name; while it seemed very likely that his last name was the same as that of his brother Jiminez, this was not stated directly in the Canon for a few volumes.
In the past he has evidently been assigned to work with/mind his brother whenever the latter fellow finds his way into contact with the Library and its personnel, a task which Aldin does not appear to relish. His superiors, on the other hand, are hinted to very much enjoy reading the resulting reports. While he is intelligent and resourceful, unlike his brother he has not yet shown any signs of being a Spark.
He enters the story when he is Agatha with her study of the Van Rijn notebook she has just donated to the Library. He comes across as being rather timid and fretful, but it is eventually revealed that this attitude is to at least some degree a . He helps/follows Agatha when she finds her way into Van Rijn's long-lost Hermitorium, and then accompanies her and her friends into the sealed ex-Corbettite artifact vaults which are present in the Library's territory, as they search for the missing Doctor Dio Zardilev.to assist
In regards to this second trip, he is engaged in a clandestine effort with the Arguron princess Larana Chroma to obtain possession of an at the time unnamed object, a fact he wishes to conceal from both his brother and Agatha. They are successful in this quest, and Aldin remains behind in the Library with the object as Agatha and her friends return to the surface. The object is eventually to be a piece of tech called "The Heart of the Muse", which is evidently the key and/or power source to a formidable-looking (but currently inactive) entity called The Muse of Vengeance.
When Agatha is later leaving Paris for Londinium, Aldin comes to say that he considers her a good person, and to give her a somewhat cryptic about the fact that powerful people are watching her closely, and she thus needs to remember to "stay a good person."
The New Heterodyne Boys
Aldin complains that his brother is always dragging him along on incredible adventures that Jiminez thoroughly enjoys and he hates, and which often result in Jiminez being seriously injured in some fashion and/or Aldin being taken prisoner and stripped of most of his clothes. (This has led Aldin to hone his lock-picking skills.) His reports on these escapades are greeted with with a great deal of  Aldin is stout in maintaining that his accounts are entirely factual, even "the thing with the naked mole rat queen". He has mentioned the titles of a few of these reports.along with a certain amount of skepticism in some quarters.
- The Adventure of the Haunted Topiary
- The Secret of the Perfectly Spherical Cow
- The Mystery of the Cyclopean Binoculars