We will never know who invented the internal gear — much less the multitude of “epicyclic” or “planetary” gear systems — but we know from archeological evidence that these versatile arrangements have been in use for a very long time. As with many gear topics there is a lot of information about them floating around the internet and — no surprise — some of it is inaccurate.
Unless you work with epicyclics on a regular basis, a “wiki” level of knowledge about them is probably sufficient. For those who aspire to master all types of gear design, there are many books and technical papers available for study. My goal in the next few postings is to take some of the mystery away and prepare the curious for more detailed investigations.