Over 200 years before Agatha's time, the "greatest Spark of the time" created a masterwork for The Storm King, Andronicus Valois: nine incredibly advanced clanks known as The Muses. The Muses had abilities to perform before an audience and create feedback to enhance or alter the audience's collective mood. This Spark's name was Van Rijn, whose full initials were RvR.
According to a footnote in the novel Agatha H. and the Clockwork Princess, Van Rijn was mysterious even in his own lifetime, with only the man's own word regarding his supposedly Dutch background. He also went out of his way to avoid having his picture painted, and so (in universe) no image of him exists. (And it's quite a long time before the reader gets even a hypothetical look at him, either.)
According to Master Payne, after Van Rijn's death (or at least disappearance, see below), many people wished to study the Muses, but the work was extremely delicate. Since these are Sparks we're talking about, this didn't stop anyone and some of the Muses were said to be tragically destroyed. To date, we've learned that five of them at least escaped being completely disassembled, though some are now rather the worse for wear. One of them, Moxana, either took with her or later acquired a notebook of Van Rijn's; based on Agatha's enthused reaction after being given a chance to read it, it is a treasure-trove of technical information. The notebook has been revealed to contain secret notes only readable when viewed in a light of the same wavelength as the King's Lightning. (Presumably the Storm King), and then even more secrets if an electrical current is passed through the metal trim of its cover.
Other Van Rijn works exist, among them an industrial sausage-works, the Storm King's powerfully electrified sword, "Archimedes' Lever" and (evidently) his zappy mace "The Platonic Solid". Agatha's acclaim (having learned from the then-current Van Rijn expert, Dr. Tarsus Beetle), indicates that any other creations would be as nearly magical.
If the notebook is be believed, its creator had an appreciation for both jam tarts and waffles.
He worked with the Corbettite Monks on their blasphemous-artifact wrangling and storage in the catacombs beneath Paris, which led to his founding the The Incorruptible Republic of the Immortal Library of the Grand Architect on the same site.
He was also an artist, creating the massive Triumph of the Storm King, a combination bas relief carving and painting currently on display in the Immortal Library; this installation also serves as a concealed lock/doorway for his personal top-secret Hermitorium. It was in this hidey-hole where he conducted work on his life-long obsession: a study of/series of conversations with The Enigma; or, as he called it, The Muse of Time. It appears he gained much knowledge from these exchanges, possibly explaining the advanced nature of his own Muses.
Perhaps more information will be coming: an author named Luceat wrote a multi-volume study on RVR entitled Life of Van Rijn, which was lost until a compete set was uncovered by that museum-based meddler Princess Neena.
Van Rijn's Finale
Near the end of his life, it appears that Van Rijn conspired with the Muse Prende to lock Andronicus in some form of temporal stasis within one of the Parisian Corbettite vaults, using yet another of his creations, Prende's Chronometric Lantern; Van Rijn also concealed the fact that His Highness's body still (technically) had life in it from his erstwhile allies, among them his apprentice Simon Voltaire. When finally released 200 years later by Agatha and Co, Andronicus considers this a betrayal, stating that Van Rijn witched him away from a battle at his moment of triumph, while Prende claims it was done to help him. Considering Andronicus's notable physical condition at the time, it was likely an attempt to preserve his life while a cure was sought for said condition. (Glowing yellow-green, venting steam or smoke, withering touch, etc etc..)
In any event, after sealing away the Storm King, Van Rijn then plotted to imprison The Enigma inside the Hermitorium, either to get help for Andronicus or to extend his own life, or both; the capture was successful, but did not result in an increased lifespan for anyone: Van Rijn in fact evidentlyin the process, and his mummified corpse remained undiscovered until Agatha manages to get into the Hermitorium. When she revives the nearly-dead/defunct Enigma, the latter individual labels her deceased captor a "presumptuous old lecher" and departs for parts or times unknown. (What a... productive... couple of days Agatha's been having!)
Possibly relevant outside information
"Van Rijn" is, in our world, the surname of the Dutch painter best known as simply "Rembrandt".