Ganymede was a Greek youth whose impossible beauty captivated Zeus.
The filthy old deity sent an eagle down to carry the boy to Olympus where he became cupbearer to the Gods and a cheeky bit of rump on the side for the Thunderer himself.
It is possibly his role as a personal servant rather than a sex slave that PG Wodehouse refers to so wittily in his Jeeves and Wooster books.
Jeeves is a member of a club for 'Gentlemen's personal Gentlemen' called 'The Junior Ganymede'.
On the other hand, perhaps PG was trying to tell us something about Bertie's relationship with his Man.
Ganymede is also the seventh and largest of Jupiter's known moons. Another classical witticism, the body was so named because 'it moons around Jupiter' (Jupiter being the Latin name of Zeus).
Can you imagine the delight of the aging, pederastic Don that came up with that one?