History of the Breed
Deerhounds are closely related to the other sighthound breeds of the British Isles, especially Greyhounds and Irish Wolfhounds. Although dogs that we would probably recognize today as being Deerhounds have existed for centuries, it is important to remember, in any historical discussion, that the notion of a breed is largely a Victorian one. It would be more correct to say that large, rough-coated sighthounds have existed in the British Isles for centuries.
It is an unfortunate fact that the work of the Deerhound--hunting the Red Deer--had ceased to exist long before the advent of our modern notion of breeds and dog shows. Although we often refer to the various Victorians, both artists and chroniclers of dogs, we must always remember that they themselves were not actually hunting with Deerhounds. Weston Bell's The Deerhound, published in 1892, reported that collies were most often used for deerstalking at that time, and that collies and collie crosses had been used almost exclusively for at least a generation. The lack of any real connection with the historical work of the Deerhound allowed the Victorians (and us) to romanticize Deerhounds beyond all reckoning. It can be hard to extract the real and the reasonable from the resulting clutter.
One of the popular romances of the Deerhound is that ownership was restricted to the nobility. The implication is that there was a set of laws somewhere that forbade mere commoners from owning "the Royal Dog of Scotland." Hunting deer in Britain was, for the most part, a pastime reserved for the nobility. Game animals belonged to the landowner, and only he (and his friends, of course) were permitted to hunt. We are not talking about a society in which pets were commonplace. If someone owned a dog, it was because they had work for that dog to do. Clearly, no one was going to own a Deerhound if he couldn't use it to hunt deer, so it only makes sense that Deerhounds were owned exclusively by the nobility.
Another common romance is that Deerhounds are a breed of great antiquity. It is certainly true that sighthounds are a type of great antiquity, and that there have been large, rough-coated sighthounds in the British Isles for centuries. It was really only in the latter half of the 19th century that careful breeding records (which in many cases existed for long periods of time) and the notion of breeding and registering dogs only when both parents were of the same breed (i.e., did the same job and were of the same type) took hold. Deerhounds as a breed are neither significantly older or younger than most other breeds.
There is also a myth of great size that is common to both the Deerhound and Irish Wolfhound communities. I am not sufficiently knowledgeable about Wolfhound history to comment on that myth, but it is safe to say that today's Deerhounds are considerably taller, and, to perhaps a lesser extent, heavier than their working forebears of, say, the 16th century. They are also taller and heavier than their direct ancestors of the late 19th century. The 19th century Deerhound mavens were inclined to believe that dogs much larger than their upper target range (which was 30" at the shoulder) were too large for work. It isn't clear to me exactly what work they were talking about, since the Deerhound wasn't routinely being asked to perform its traditional work after sometime in the 18th century, but it is certainly clear that the dogs who were doing their traditional work, back in the days before accurate long-range rifles and ultimately the modern cartridge-firing rifle, were substantially smaller than today's Deerhounds. Some of the dogs were 26" or 27" at the shoulder, and weighed no more than 65-75 pounds, while the bitches were even smaller. Today, bitches average just under 30", with dogs around 32". Did we selectively breed for greater height? Unquestionably. Did improvements in medical care, antibiotics and nutrition play a role? Unquestionably. Can we estimate the relative contribution of these two influences? No, although we can argue about it until the cows come home. Are today's dogs too big for work? Maybe; but many of today's large males are excellent lure coursers (a sport arguably designed for the significantly smaller and thus more agile Greyhound, and at which the premier athletes are generally acknowledged to be the even smaller and more agile yet Whippets). In the absence of the widespread availability of red deer hunting (with Deerhounds), at least some Deerhound breeders routinely test their dogs at other running sports (lure coursing, straight and oval racing, and open field (live game, generally hare or jackrabbit) coursing), and the best of today's dogs, even big ones, acquit themselves well.