I couldn't think of a Beatles related name I liked, and I liked how that one member always comes up as a guest, so I went with unknown. It's also kind of a reference to a quote by Ronald Rumsfield my dad had on his fridge for the longest time, that always intrigued me as a kid.
"There are known knowns; there are things we know that we know.
There are known unknowns; that is to say, there are things that we now know we don't know.
But there are also unknown unknowns – there are things we do not know ...