From the history of the breed: 
The direct ancestor of the boxer is considered to be or Brabanter Bullenbeissers. At that time the breeding of Bullenbeisser was mainly in the hands of hunters who used them for hunting.

Nylon Training Dog Harness for Boxer

Bullenbeisser's task was to catch an animal hunted by hounds and hold it until the arrival of the hunter that killed the prey. For this purpose the dog should have had broad jaws with broadly-set teeth in order to bite hard and hold the prey tightly. Each Bullenbeisser, who had this feature, was primarily used for breeding. Thus the breeding selection was conducted, which resulted in a wide-muzzled dog with upturned nose. 

General appearance: 
The boxer - is a dog of above the average height, smooth coated, sturdy, square in size, and with strong skeleton. The musculature is taut, strongly developed, moulded in appearance. The moves are lively, full of strength and nobility. The Boxer is not supposed to look awkward or clumsy, or to look light. 
Height and weight: 
Height: Males 22 - 25 inches (57-63 cm), Females 21 - 23 inches (53-59 cm) at the withers. 
Weight: Males: over 66 lb (30 kg) (with the height at the shoulder of about 24 inches (60 cm)). Females: about 55 lb (25 kg) (with the height at the withers of about 22 inches (56cm)). 
Body proportions: 
Square built. 
Coat: 
The coat is short, skin-tight, tough and shiny. 
Color: 
Fawn or brindle. Fawn of various shades is permitted - from light fawn to reddish-brown, however, middle range (red fawn) are the most preferable. 

Head: 
Makes the Boxer look uniquely; it should be in correct proportion to the body and appear neither light nor too heavy. The muzzle should be as broad as possible and powerful. The beauty of the head is provided due to the correct ratio of the muzzle and the skull. During the examination of the head from any position: top, front or side - the muzzle should remain in correct proportion to the skull, i.e., it should never look too small. The head should be clean, with no wrinkles. However, the natural folds appear on the forehead spontaneously when a dog raises his ears or if the ears are not docked when alerted. From root of nose wrinkles are always indicated running in a downward direction on both sides. The black mask is located only on the muzzle area, sharply contrasts on the basic color and should not give sombre expression. 
Ears: 
Have an appropriate size; are set on each side of the head at the highest part of the skull, when in repose fit closely to the cheeks and turn forward when the dog is alert, with clearly expressed fold. 
Eyes: 
Dark, not too small, protruding or deep set. 
Teeth: 
The lower jaw is longer than the upper and is slightly curved upwards. Form of the Boxer's bite is undershot. The upper jaw is wide at the base and slightly tapering towards the end. Teeth are strong and healthy. The incisors are located right in one line as far as it possible; the canines are large and set wide apart. 
Neck: 
The ridge of the neck falls from the occiput to the withers by an elegantly curved arch. The neck should be long enough, round, powerful, muscled and taut. Body: The withers should be well expressed. The body from the withers to the croup should be short, firm, smooth, wide and very muscular. The croup is slightly sloping, is a bit rounded, broad. Pelvis should be long and wide, especially in females. 

Chest: 
Deep, reaching to elbows. Depth of chest is half of the height at the withers. The front part of the chest is well developed. The ribs are well arched but not of a barrel shape, extending far back. 
Belly: 
Underline stretches back in an elegant bend. The groin is short, moderately tucked up. 
Limbs: 
Forequarters should be straight when viewed from the front, should be parallel to each other and have strong bones. 
Hindquarters are well muscled, the muscles are tight and very expressive. The hind limbs when viewed from behind should be straight. 
Tail: 
Set high enough. 
Attractive features: 
Smart, disciplined, steady, calm and watchful and at the same time, self-confident, fearless and enduring dog. The type of behavior is balanced - agile. The Boxer retains the honesty of the character and deprived of malice, even in an old age, when other dogs often become "grumblers". Despite a rather intimidating appearance, the Boxer is tender and affectionate, likes children and gets along well with them. He is faithful to his master, tied to the entire family and home. This is a courageous defender, gentle with friends, but distrustful to the strangers, cheerful and friendly in play, but fearless in the attack. The Boxer inherited nobility and courage from his ancestors. He has an honest and open disposition, without falsehood and treachery. This dog is very amenable to training and is very understanding. He is easily trained due to his willingness to obey, his courage and fighting qualities, natural sharpness and excellent sense of smell. The Boxers are unpretentious and cleanly and therefore can be kept in the apartment/flat.