Brutus (Universal Monsters)
Brutus was a large dog kept as a pet by scientist Peter Drury. Brutus acted as Dr. Drury's loyal guardian, and was also used as a test subject for his invisibility experiments. Brutus was made invisible by his owner, and then visible again by means of a total blood transfusion from another dog (which unfortunately cost the other dog its life, Drury discovered).
After the invisible Robert Griffin knocked out Drury and took his blood to become visible again, killing him, he set Drury's house on fire and fled. Brutus however escaped from the burning house and pursued Griffin, and for the next several days hounded him day and night at the Herrick mansion, despite Herbert Higgins' attempts to get rid of the animal. Eventually, Brutus got away from Higgins and gained entrance into the Herrick home, where he surprised Griffin (who had turned invisible again) trying to take the blood of Mark Foster. Brutus attacked and killed the unprepared Griffin.