The Point of Origin
At the epicentre of Primus the cyclonic eruption of creative & destructive force from the Motive, and the raw physical elements from the Material, explode through into the Medium.
At first, the explosion seemed chaotic. However, the energy and material soon cooled and formed a shell of interlocking and overlapping plates. These plates disrupted and refracted the energy continuing the pour out of the rift in the Astral Sea, splintering them, and sending different amounts of good, evil, and the base elements into each plane.
As time went on, the plates turned, driven like crude fans might when blown by a mighty gale. More and more layers were gradually accreted to the shell, and eventually they began to form an ordered machine that looked more like a enormous clock, and less like a pile of scrap metal.
As the machine ticked and grew, it became slowly more and more complex. The rhythms and waves of actions that ripples across its surface began to replicate and take on self-motivating characteristics until... it had an idea.
The idea was simple. Grow.
And so it did, consciously and deliberately. No longer just a random factory of random planes spilling out into the Astral Sea. Now it began to take on the characteristics of a cosmic endoplasmic reticulum, creating ever more complex structures out of the chaos that it could use to add ever more layers to its shell.
This idea had a name: Primus.
A factory needs workers, a series of static machines is inefficient for doing the finer work of sorting, folding, and compartmentalising and recombining chaos into ordered outputs.
Then, once the fields have been sown, and the crops matured, something must harvest the plants, thresh the grain and remove the unnecessary chaff, and process the product into what Primus needs in order to grow.
These workers are the modrons.
Modrons, when they are outside Primus are indeed harvesters, of a kind. They principally seek out artefacts of unique creativity or complexity, often the work of other conscious beings that have come to inhabit the planes created by Primus, in order to bring them back as examples to inspire Primus in their next project. For this reason, Primus seeks to create planes that are conducive life. However, Primus has also learned that planes that are too abundant and peaceful tend to be inhabited by creatures with no desire to imagine new machines. Therefore, Primus tends to crease universes with ample opportunity for conflict between the forces of good and evil.
Modrons don’t really care who or what they need to break outside of Primus to obtain interesting artefacts, which occasionally means kidnapping interesting minds. If you’re ever wondering why extremely accomplished wizards tend to hide in their towers and don’t just solve every issue with a snap of their fingers, it’s probably because they’re trying not to attract the attention of Primus. Even Gods, in whatever form they take across the multiverse, are not immune to unwelcome interference by swarms of Modrons, and tend to favour indirect subtle influence, rather than impressive feats of miracle working.