Spike is the pet dog of the Pickles family and has a very strong friendship with Tommy. He is a recurring character on the show and is always willing to help the babies (or, in the case of the episode "Potty Training Spike", the babies are willing to help him). Spike appears in all three Rugrats films but his most prominent role came in Rugrats In Paris, in which he meets Fifi, who becomes his mate in every episode produced after that film. In the third film, Rugrats Go Wild, Spike meets Eliza Thornberry, therefore gaining the ability to speak English, but like with every other animal Eliza can talk to, only she (and the chimp Darwin) can understand him.
It is revealed at the end of the episode "Spike Runs Away" that Spike is a fictional breed known as a Siberian Tiger Hound. Apparently the breed is very rare and worth thousands, according to his rescuer, Winston St. George.