According to Brian Patrick Duggan, in his book Horror Dogs: Man’s Best Friend as Movie Monster, the first dog in a motion picture appears in Edison’s Athlete with a Wand in 1894; but that dog just happened to be in the shot, lying at the foot of the athlete doing all the work, so he points us to Rescue Rover (1905), for a more action-oriented Collie. That family canine as rescuer theme leads us to Rin Tin Tin and more stories of dogs leaping into action to save us dumb humans or battle evil humans too, in movies, comics, and books. Of course, the horror genre has morphed the family-oriented dog to terrorize us, chase us, tear us apart, and, in general, make us run like hell or scream like hell. Rin Tin Tin was not a scary dog. Going to 1904, in Edison’s Dog Factory, the first hint of making dogs scarier, if only in a comedic way, can be found. Duggan goes on to note how the movie poster advertising began to show the dog as dangerous (in a wholesome way). By the time we get to 1978 and Devil Dog: The Hound of Hell, the movie poster art focused on those sharp canine teeth a lot more, which was definitely not wholesome.
Rin Tin Tin’s predecessor, Strongheart, starred in six films from 1921 through 1927, but just two of those posters show the dog only launching himself at bad guys. From 1922 through 1931, the more famous Rin Tin Tin averaged even fewer examples, with only three posters out of twenty-six showing him poised just prior to grappling with the film’s villain. The implied canine violence in advertising and what was shown on screen was justifiable, because Strongheart or Rin Tin Tin were protecting their people or meting out canine justice. (Duggan, Brian Patrick. Horror Dogs: Man’s Best Friend as Movie Monster (Dogs in Our World) (p. 103). McFarland & Company, Inc., Publishers. Kindle Edition.)
End Note: Warner Brothers originally had the popular Rin Tin Tin, but dropped the poor dog because of sound issues and their focus on talkies with humans. That’s when Mascot picked up the franchise with their first all-sound serial Rin-Tin-Tin The Lone Defender. Clearly they didn’t worry about his barking.