These massive, heavy-boned dogs have thick muscles which are covered by a double coat of fawn, apricot or brindle stripes. According to the AKC, English Mastiffs are lovable companions but a formidable protector of their owner. A natural wariness to strangers makes early training and socialization a must. Mastiffs can be as large as 30 inches tall and can weigh over 200 pounds. Mastiffs have large heads, wrinkled foreheads, combined with a kind and alert expression.