He was portrayed by the late Chuck Connors.
Janos was bloodthirsty werewolf who had been bitten as far back as at least the 19th century by a much more powerful werewolf by the name of Nicolas Remy. Although it is hinted he did not get along with his master give Remy had cut out his left eye for punishment.
Janos grew to be a very powerful werewolf and could transform at free will. His transformation process was unique given he simply ripped his human flesh off with his inner wolf emerging from beneath. He also didn't seem to age, given he had been bitten sometime in the 19th century when he was in his twenties, and appeared to be only in his sixties in 1987. Janos proved to be the most monstrous of the werewolves on the show. He killed for his own amusement and seemed to cures others because he enjoyed seeing them lose their humanity. He worked as a sailor so he could go from place to place to kill as many people as possible.
One night, a young college student named Ted was wandering around his dock at night. Fully transformed, Janos attacked Ted and turned him into a werewolf. Unable to control the urges of the wolf as he began killing innocent people and not wanting to lock himself up, Ted had his best friend/roommate, Eric Cord, stay with him one night to shoot him once he changed. He does so, but not before Ted bites him and passes the curse onto him.
At some point, Janos killed a couple in Sana Clara while Eric was locking himself up. Believing Janos to be the Werewolf that began his bloodline, he goes to Janos' dock to get more information. He meets Janos, and tries to convince him he's merely interested in working for him. Janos is not buying it, and is well aware that Eric is a werewolf. Eric is terrified of him and runs away. He then tries to have his girlfriend/Ted's sister, Kelly lock him up in the bathroom of an apartment. She ties his hands together and locks him in, but Janos has been stalking him and kidnaps Kelly to take her to his cabin in the woods. He attempts to kill her, but Eric transforms and tracks him down to his cabin. Janos transforms and the two fight long enough for Kelly to escape. Janos overpowers Eric and then manages to escape himself, unable to find Kelly.
Eric never stopped trying to find Janos. In Nightwatch, he tracks him down to a shipyard, where Janos murders another sailor who was suspicious of him. In The Black Ship, Janos has an old friend, Otto Reinfield, kidnap Eric and promises him he will bite him and give him immortality in return. Otto captures Eric, but once he witnesses the monster Janos is, he changes his mind, but Janos bites him anyways. Otto has Eric shoot him death once he escapes.
In Friendly Haven, Eric tracks him down these woods that people have claimed contain "Bigfoot" sightings, when in reality, it is Janos killing hunters. Janos also appears in The Unicorn were he killed at least nine prostitutes by pretending to be an ordinary customer, only to brutally murder them once they take him to their rooms for the night. Janos appears briefly in A Material Girl where Eric attempt to kill him at a mall, but fails to do so and Janos escapes.
Janos made his final appearance in part 1 of To Dream of Wolves, where Eric finally discovers that Janos is not the originator of the bloodline, but a priest, names Nicolas Remy is. Eric fights Janos, throws acid in his face, and electrocutes him, which supposedly kills him. Though Janos appears dead, his body is nowhere to find in that same place when Rogan shows up in the same area. Whether or not Remy disposed of his body, or Janos did in fact survive and leave, is up to speculation.