The Haunted Mansion has a large cast of characters, but it's definitely a circumscribed group. When the Ghost Host claims that they come from "all over the world," that's a bit of a sham. They come from Northern Europe and North America, with the exception of three from the Mediterranean basin: Caesar and two Egyptians (viz, the graveyard mummy and the Cleopatra-like lady on the chandelier). Someone may ask whether even that is too generous a description. Since a Victorian gentleman or gentlewoman who doesn't open his or her mouth could hail from either Old England or New England, how do we know there are any North Americans at all? Well, we're in New Orleans, and whole flocks of wraiths are pouring up out of the graveyard, so presumably most of them are Americans. We can thank Ken Anderson for that element (including how the effect is done—projections on a scrim).
But better still, there is one ghost in there who is plainly North American (hint: Paul Frees is Canadian).
No East Asians, no sub-Sahara Africans, no Native Americans, no Pacific Islanders, etc. Does it mean anything? I suspect that it signals a restriction on what kind of ghost traditions we are supposed to presume in the HM. Sure, cultures all over the world believe in ghosts, but spirits of the dead in China or among Native Americans are regarded differently and function differently within those cultural-religious matrices than do our familiar Euro-American ghosts. Reportedly, this is one reason why the Hong Kong Disneyland isn't getting anything similar to the Haunted Mansions found in all the other parks. Within the Euro-American world, we assume that spirits of the dead are normally gone and out of our sphere, in heaven or hell or somewhere like that, and if they come back it's because something is wrong somewhere. Something needs to be done so that they can rest in peace like they're supposed to. If you should happen to see one, it is normally cause for concern, for dread.
If you're a storyteller you have to draw the circle somewhere or you won't have enough common ground with the audience to tell any kind of narrative, however vague. Without the usual Euro-American expectations about ghosts, the whole joke of the Haunted Mansion fails miserably.
So much for space; what about the other variable of existence, time? Plainly we've got ghosts from many different ages cavorting before our eyes. Apparently the afterlife opens up a pool of potential partners that eHarmony.com can only dream of. A medieval soldier is starting to get a little jiggy with that aforementioned Egyptian lass, the one with the Great Pyramids.
If we're looking for the oldest ghosts in the place, our three Mediterraneans easily take the prize. There's this Egyptian gal, and of course our old friend Caesar down below her...
There are a good dozen or so medieval figures, but the vast majority of the ghosts we see appear to be 19th century vintage, and most of those Victorian, presumably because so many ghost stories seem to take place in such a historical setting, and because ghosts of that era no doubt feel at home in a house of comparable age.
A more interesting question is, which ghost is the youngest, the most modern? The Imagineers seem to have restricted themselves in this area too. There are no 20th century ghosts. You might think that, well, what kind of distinctly 20th c. characters could have been offered that would have humorous potential and be instantly recognizable? Plenty! Where's your imagination? A World War I doughboy, a flapper, a Chicago gangster of the Machine-Gun Kelly/Edward G. Robinson type. Marc Davis could have spun out a dozen of these before breakfast, but they're not there. I think it was a conscious limitation.
My vote for the youngest ghosts goes to the bicyclists. They're a little loopy, but they're favorites with many fans. Another Davis idea, too.
The tandem bike as we know it was invented in 1898, so there you go; they're perched right at the outer rim of the 19th century. Lest you think this is pressing the details a bit hard, I call your attention to a seldom-seen concept sketch by Davis showing that he was perfectly conscious of the late-90's setting of the tandem bike.
One of the brighter spots in the otherwise disappointing 2003 movie adaptation of the Haunted Mansion was the decision to recast the singing busts as a barbershop quartet and enlist the current incarnation of the Dapper Dans to provide the voices. Who does NOT like the Dans, anyway? I think it's a kick to have Davis's sketch before you as you listen...
Grim Grinning Ghosts - The Dapper Dans
So for what it's worth, there you go; there are the parameters for the cast of characters used to tell the Mansion tale.