Sherlock Holmes (Benedict Cumberbatch) will go head to head with a new villain in the upcoming season named Culverton Smith. The Holmes' other brother — Sherrinford — might pay his brothers a visit in Baker Street.

Culverton Smith (Toby Jones)  was introduced as the new villain in the "Sherlock" season 4 teaser. Smith — who is expected to be the most evil out of all of Sherlock's enemies — was shown to be having an intense conversation with the consulting detective while he's in a car with Dr. John Watson (Martin Freeman).

Little detail was revealed about Smith's villainous ways, but he will be the darkest antagonist on the show yet according to showrunner Steven Moffat.

At the San Diego Comic-Con last July, Moffat and co-showrunner Mark Gatiss explained how Smith will be different from Sherlock's previous enemies. Moffat explains that while Jim Moriarty (Andrew Scott) was somewhat charming and Charles Augustus Magnussen (Lars Mikkelsen) was fascinatingly amoral, Smith will be pure evil and appalling.

"Toby is doing something very interesting. He's an avuncular, funny seeming man with terrible teeth. We've given him terrible teeth, which are symbolic of the rot inside him. It's a great complex, shaded character," Gatiss explains.

Speculations arose that the unseen Holmes brother will be appearing in season 4. At the San Diego Comic-Con last July, the cast of "Sherlock" displayed three names that could be appearing as new characters in the upcoming season.

One of the names is Sherrinford, the hypothetical third Holmes brother. Rumors abound that the character will be played by Tom Hiddleston. These rumors were boosted when Gatiss — who also plays Mycroft Holmes — posted a photo of him with Hiddleston and Amanda Abbington on Twitter.

Lifestyle reports that series regulars Cumberbatch, Freeman, and Gatiss will definitely be returning in "Sherlock" season 4. Fans can also expect Abbington as Mary, Rupert Graves as Greg Lestrade, Una Stubbs as landlady Mrs. Hudson, and Louise Brealey as Molly Hooper.

"Sherlock" season 4 premieres January 2017.