History
The Boxer breed of dog was developed in Germany in the 1800s from several other breeds, such as the Great Dane, Bulldog, and Mastiff. Apparently the Germans just couldn't get enough deadly fighting dogs. Not to say that the Boxer is by nature a vicious animal, most are very friendly. They were, however, bred to fight. In fact, the name Boxer is derived from the way the dog strikes with its front paws in combat. It was intended for fighting, hunting, and bull-baiting. The dogs were also used for everything from pulling carts to performing in circuses. In 1904 the American Kennel Club first recognized the breed, and its first championship was finished in 1915. The Boxer is in the working group of dogs.
Appearance
Boxers are medium-large dogs, around 50-75 pounds and 21-25 inches tall. Their bodies are very lean and muscular, with taut skin and a short coat. Their fur is either fawn or brindle (a pattern of odd brown and black stripes and spots), with black snouts and white underbellies and chests. Sometimes the white markings extend onto the face. According to the AKC, if white fur covers more than 1/3rd of the body, the Boxer is disqualified. I once met an all-white Boxer, but it was probably part Pitbull, or some sort of genetic defect. In addition, most Boxers have their tails chopped short and their ears propped up at an early age. Recently many owners have begun to see this as cruel and have stopped doing one or both. Of the three Boxers I've owned, one had her ears up and tail docked, one had his ears down and tail intact, and the current one has her ears down and tail docked.
Temperament
The Boxer should be confident, happy, playful, curious, and very energetic. They are very loyal and affectionate dogs. In my experience they have gotten along very well with people, including (especially) children, but not very well with other dogs. My second Boxer, Sport, was the neighborhood bully and beat up every dog he could get his paws on. Boxers are excellent guard dogs.
References:
http://www.akc.org/breeds/recbreeds/boxer.cfm
http://www.dogbreedinfo.com/boxer.htm