Watson appears as an anthropomorphic Scottish Terrier with a slightly overweight physique. He acts as Sherlock Hound's loyal companion and assistant, sharing their Baker Street residence. Trained as a medical professional, he returned to England after military service.

His personality blends unwavering dedication to Hound with a generally friendly demeanor. He actively engages in investigations but occasionally lags behind Hound physically during chases or struggles to match his deductive pace, creating lighthearted contrasts. Watson harbors romantic feelings for Mrs. Hudson, their young widow landlady—a dynamic complicated by rival affections from Hound and Professor Moriarty. He operates a distinctive yellow automobile featured in pursuits against antagonists.

While skilled in medicine, Watson lacks Hound’s exceptional deductive abilities; his investigative contributions emphasize practical support over analytical breakthroughs. During clashes with Moriarty’s henchmen Smiley and Todd, he participates actively but rarely drives resolutions. His role remains consistently supportive across all documented media, with no evolution in core traits or relationships.

Watson features identically in the 26-episode television series and subsequent compilation films, maintaining his established portrayal without added backstory or development.