Dukey is a mixed-breed dog belonging to the Test family. Due to genetic enhancements by Susan and Mary Test, Dukey is highly intelligent and capable of speech. To take advantage of the widespread low intelligence and/or common sense of the show's inhabitants, Dukey claims himself to be a human with a rare hair disorder to throw off any suspicion of his true nature. Dukey would act as the voice of reason to Johnny, Susan and/or Mary Test if any of them actually listened to him. Despite Johnny's overwhelmingly callous and selfish behavior, attempting to do harm to Johnny's well-being is known to set Dukey off.
Dukey is voiced by Louis Chirillo for the first four seasons of the show. Due to Chirillo's retirement from voice-acting, Trevor Devall took over the role starting with the fifth season.