A group of casual gamers. Mercury, the element, is befitting of gaming, its heavy, its metal, its fluid, and its symbol, Hg, is also fitting. Mercury started up around 2014 on a small home server hosting TS3 and a few game servers. It evolved from there, hosting a website briefly to link admins to the server machine. This all well before the release of Discord, was either paid for, or DIY, so the stability of things was shaky at best.
When Discord released, it's own launch was sketchy, initially the founder was strong against Discord due to a privacy discrepancy that nearly allowed them freely snoop through your PC's contents. Once that was sorted out and corrected though, Mercury warmed up to the advantage of a free community hub.