Oliver Wendell Holmes (Sr.) is generally credited as the first to call the Massachusetts State House "the Hub of the Solar System". Soon enough people (mostly newspapers, really, eager as always to shave three letters off a headline) started using "the Hub" to refer to Boston as a whole, and for some reason it tends to get expanded as "the Hub of the Universe" these days.

Strangely enough, actual people who actually live in the actual city of Boston seem to call it "Boston" instead.

The original Holmes quotation goes like this:

Boston State-house is the hub of the solar system. You couldn't pry that out of a Boston man if you had the tire of all creation straightened out for a crow-bar.

and appears in his Autocrat of the Breakfast Table, a series of columns in the Atlantic Monthly later collected in book form.

As ellF reminds me, Boston is also at the center of the ring roads Route 128 (mostly Interstate 95) and Interstate 495. As in many other cities, the fraction of its road system that is vaguely modern is laid out in a hub and spoke topology, except for the big bite taken out by the Harbor, so we could point to a map and call ourselves the Hub of the Boston Area if we were inclined to modesty.