I’ve heard two histories of the boxer dog.
One of them is just as Megargee describes it– a dog like a dogue de Bordeaux that was bred down into a German boar catcher.
I’ve even heard it suggested that the South African boerboel is actually almost entirely derived from the Brabanter bullenbeisser, which supposedly looked like a bullmastiff or dogue de Bordeaux in its original form. However, there is also a lot of evidence that the boerboel’s affinity with the bullmastiff comes from heavy crossbreeding from bullmastiffs that were imported by the De Beers diamond company.
I don’t know enough about boerboels to vouch for the veracity of either theory, but I do think there may be a bit of an error in assuming that the boxer was just a bred down dogue de Bordeaux or bullmastiff.
My take on it is that the original bullenbeissers were actually virtually indistinguishable from the dog that we call the Alano Español or “Spanish bulldog.”
Here’s an image of a modern alano:
And here are German bullenbeissers on a boar hunt:
And here is the famous image of a German bullenbeisser:
I would even go as far as to suggest that the bullenbeissers and the alano are actually the same breed. If you think about it, it may have been that the Spanish introduced this dog to the Low Countries, which Spain once ruled, and to parts of the German-speaking world, where the Spanish and Austria Hapsburgs ruled various kingdoms and principalities.
The bullenbeissers of yore and the Spanish bulldog of today are both larger than the typical boxer, which was bred down through the use of English bulldog blood, but that was not to produce a hunting or working dog.
It was to produce a fancier version of the bullenbeisser type. Stockmann, the man quoted in the piece, actually was instrumental in changing the bulldog-type boxer back into something longer-legged and more athletic, a dog more suitable for use as a sentry and messenger dog in the First World War. (Stockmann’s prose in the preceding link is probably the best description of boxer dog behavior and attributes that I’ve ever read.)
The boxer went from being the bullenbeisser to the bulldog cross show dog back into a working bulldog.
Stockmann was correct in saying that the boxer was bred down from the bullenbeisser, but the bullenbeisser was not like a dogue de Bordeaux, a Bullmastiff, or a boerboel. It was more like a big alano-type bulldog.