English folklore has the ominous legend of the Black Dog (the Grim), a beast whose appearance presages doom, death, or, at best, despair The Black Dog can be a symbol of evil. It is more commonly an omen of something bad to come. Bad luck from the olden days when Europe and the British Isles were pagan. Pre-Christianity. Some seem attached to families, while most are rather random but specific to their locality.
But there are also reports, some of them first-person, of wayfarers (especially lone females) being protected by Black Dogs. There is also a legend of a benevolent Black Dog, who appears to guide travelers to a safe haven. Black dogs are sometimes seen as guardians of a soul when it travels between planes and such.
(Source: darren-kryptonite, via theladystache)