"Rhencius" is the Latin term for the river "(the) Rhine", which I spent a lot of my childhood around. And in memory of those days, I decided to name myself after it. However, "Rhencius" [Ran-cious] is hard to pronounce for many people because of the ending, so they started calling me "Rhen", which I then thought was both easier to pronounce and remember, so I went with that.