Warning: SPOILERS for Cobra Kai Season 4.
A joke about Terry Silver (Thomas Ian Griffth) resembling the Highlander set up Cobra Kai season 4's ending twist with John Kreese (Martin Kove). The villain from The Karate Kid Part III, Terry Silver was recruited by Kreese to serve as Cobra Kai's co-sensei and counteract the alliance between Daniel LaRusso (Ralph Macchio) and Johnny Lawrence (William Zabka). But Silver put his own machinations into motion to supplant Kreese as Cobra Kai's sole leader, and a wisecrack about Highlander foreshadowed Terry turning on his old Vietnam war buddy.
Highlander began as a 1986 film starring Christopher Lambert and Sean Connery about sword-wielding immortal warriors Connor MacLeod and Juan Sanchez Ramirez. The franchise introduced its trademark catchphrase: "There can be only one." Despite not being a box office hit, Highlander's intriguing concept spawned three movie sequels, a planned Highlander movie reboot starring Henry Cavill, and a TV spinoff, Highlander: The Series, which starred Adrian Paul as Connor's Scottish kinsman, Duncan MacLeod. The Highlander TV show was a cult favorite that ran for 6 seasons in the 1990s and Paul was a handsome, ponytailed martial artist whose Duncan surpassed Connor in popularity as the Highlander. However, The Karate Kid Part III hit theaters in 1989, and Terry Silver brought Duncan McLeod's signature ponytailed look to the big screen three years before Highlander: The Series even debuted.
When Terry Silver and John Kreese invaded the Miyagi-Do dojo in Cobra Kai season 4, episode 5, "Match Point," the combined students of Daniel's school and Johnny's Eagle Fang karate huddled and watched as the Cobra Kai interlopers confronted their senseis. None of the teens knew who Terry Silver was (and neither did Johnny), but Bert (Owen Morgan) realized Terry's resemblance to Duncan MacLeod and said, "He looks like a Highlander." Nathaniel (Nathaniel Oh) corrected his friend and replied, "*The* Highlander. There can be only one." While this is a funny line that's just one of the numerous 1980s pop culture references in Cobra Kai, it also has greater significance and lays the groundwork for Silver's shocking betrayal of Kreese in Cobra Kai season 4's finale.
Surprisingly, despite outward appearances, Kreese and Silver were not the bosom buddies in Cobra Kai season 4 that they were in The Karate Kid Part III. Terry had changed in the three decades since their plan to humiliate Daniel failed. Silver admitted that he was high on cocaine in the 1980s and that his plot to harass the teenage LaRusso and force him to enter a karate tournament was "insane." But there were also deeper, unresolved issues between Kreese and Silver going back to their Vietnam days, as seen in season 3's flashbacks of Cobra Kai's origin. While Terry was grateful John saved his life from the Viet Cong, he secretly resented how Kreese held the guilt over him for the rest of their lives and this motivated him to stab his old friend in the back to take sole control of Cobra Kai.
By the end of Cobra Kai season 4, Terry fulfilled the famous Highlander credo - "There can be only one" - when he framed and had Kreese arrested for the attempted murder of Stingray (Paul Walter Hauser), who was Silver's willing accomplice. With Kreese carted off by the cops, Terry became his own version of the Highlander by making it so that "there can be only one" sensei of Cobra Kai. Of course, this evil deed is something neither Duncan nor Connor MacLeod would ever do since the two Highlanders fought evil immortals for hundreds of years. But typical of its clever writing, Cobra Kai's Highlander reference was more than a witty quip and it slyly set up Terry Silver's rise to become the Big Bad of Cobra Kai season 5.
Cobra Kai Season 4 is streaming on Netflix.