James Horton is a major villain in Highlander : The Series and the closest thing Duncan Macleod had to a true archenemy. He is was a Watcher and the leader of The Hunters, a cult-like faction of renegade Watchers that sought to wipe out all Immortals, whom they considered abominations that had to be destroyed. From 1981 to 1985 he had been the Watcher for the vicious immortal known as The Kurgan, one of the most brutal Immortals ever recorded, which may have influenced Horton's belief that Immortals had to be eliminated.  The sheer amount of pain his activities caused for Macleod and his friends cannot be discounted.

He was portrayed by Peter Hudson.

Unlike most of Macleod's major foes, Horton was mortal, a renegade of the secret organization of Immortal observers, The Watchers. He had married into Joe Dawson's family, and used him to gain access to the files of other Immortals. Forming the Hunters from other disaffected Watchers, Horton began a reign of terror meant to ensure that no Immortal ever took the Prize meant for the last one of their kind, since it was believed that this Immortal would gain power over the entire world. Ironically, by the time Horton, Dawson and the concept of the Watchers appeared on the TV series, the concept of the Gathering, the last battles of the final handful of Immortals, had been utterly de-emphasized, to the point where only the catchphrase/mantra "There Can Be Only One" remained, with little or no reference to The Prize. Even Connor Macleod's epic battle with Kurgan had been relegated via retcon to being merely an important battle in Immortal history, instead of the very last deciding one. Now, new immortals would begin to emerge, and Horton and his followers would stalk them all, believeing them a monstrous challenge to Humanity's very worth. With his very first known strike, Horton fixed his place in Highlander history and established his villainous credentials in the worst possible way.

With the zeal of every crusader fanatic throughout known history, he targeted Father Darius, a former barbarian conqueror turned Holy Man, and an immortal mentor to Duncan Macleod. A pacifist who had rarely left holy ground since his conversion to loving peace, Darius spent nearly all of his time at a Paris church, promoting organizations that fought for peace. In Horton's eyes, he was a prime target, one he and his henchmen saw as manipulating mankind for two thousand years, and perhaps also because Darius was said to have become the man he did by killing another pious, peace-loving elder Immortal, being "lightened" by his essence (much as Duncan would one day suffer from the accumulated essences of the evil Immortals he killed). Since such a redemptive story ran counter to his bigoted propaganda, with Darius Horton would move his operations out of the shadows against this great man.

Many of the Immortals killed by Horton and the Hunters remain unknown; during one, an immortal couple were too close to each other when the wife was killed, charging up her grieving husband and enabling his escape. Learning from this, when Horton moved to kill Darius, he made certain no other Immortals were present, having his spies keep an eye on Darius' known associates, including Duncan, his fiancee Tessa Noel, the pre-Immortal Richie Ryan, and Macleod's dear old friend, Hugh Fitzcairn, who had come to him concerned about several old friends vanishing without a trace, past the usual patterns Immortals had of doing so. Perhaps sensing that something was amiss, Darius had previously mailed Duncan several Watcher journals, though how he came by these is unknown. This alerted Macleod and his friends that they were being watched, and indeed, had been, perhaps throughout their whole lives. At one point, one of Horton's agents even deliberately scratched Tessa to see if she was an Immortal.

The battle in which Darius was killed was not shown, but his friends found him, and painfully realized that, not only was he dead, but the lack of any other Immortals in the vicinity meant that there was no Quickening, meaning that all of Darius' knowledge and wisdom was forever lost. Macleod and Fitzcairn were next on his list.

While Duncan's recent return to the rigors of "The Game" had him prepped enough to handle the Hunters and protect those closest to him, Fitzcairn had been out of it longer and ended up captured. To be certain of their prey's identity, they ran him through and waited for him to revive. Horton revealed several cold facets to his personality as Fitzcairn learned in horror that this practice was standard procedure for confirmation of Immortals, meaning that many innocent mortals had died this way. Faced by Macleod as he rescued his friends, Horton sacrificed a few of his men as he got away.

Macleod's efforts to find Horton's whereabouts did not go unnoticed by his own Watcher, Joe Dawson, who chose at this time to ease Macleod's concerns by revealing the existence of the Watchers, their mission and purpose. While Dawson had realized that Duncan already knew that there was such an organization, he firmly disbelieved Macleod's accounts of Immortals slain by rogue Watchers. Macleod was able to talk down one Hunter, and persuade him not to throw his life away, but the mercy he then showed Macleod cost him his life at Horton's hands, even though this man was his daughter's fiance. His crimes exposed, Horton all but bragged of his crusade and called Dawson a naive fool. An enraged Macleod ran him through, leaving Horton's daughter to be comforted by her Uncle Joe. Yet all was far from done.

Horton had in fact survived, with Joe aiding his brother-in-law by getting him medical aid and faking his death with the promise that he avoid both the Hunters and Macleod. Perhaps Joe really was naive, for he accepted Horton's word and then quickly lost track of him, his activities resumed and redoubled, though with the most sinister twist to date.

Whether at his specific direction or simply by the plans he had laid out, the Hunters soon struck at Macleod once again, and this blow would be felt deeply by the Highlander. This group would allow Immortals to fight, but in pitch darkness while the Hunter wore night-vision goggles. After several Immortals were lost in this way, a chance encounter with one of Richie Ryan's ex-girlfriends led to her grim psychic reading : Macleod would face an opponent hidden by darkness and Richie would die. Like each of the other fallen Immortals, Duncan found those closest to him - Richie and Tessa - kidnapped and held as bait. After freeing his friends and killing several of their ruthless captors, Duncan went to face their leader in the darkness. At a precise moment, Duncan used his sword to light a book of matches in front of his foe, blinding him from the glare caused by his light-magnification goggles. Killing him, Duncan went to rejoin his loved ones. Sadly, a mugger, unconnected to the Hunters in any way, shot Richie and Tessa while trying to rob them. Richie revived and was now Immortal; Tessa did not.

Horton's next set of schemes bypassed their attention-getting methods of times past. Using ruthless Immortal Xavier St. Cloud, an enemy of Duncan's who lost an arm to him in combat, he stalked several immortals, now able to sense them without capture, and riddling them with gunfire to make St. Cloud's task an easy one. St. Cloud, whether he believed it or not, had been promised the Prize if he cooperated. But however stealthy Horton thought he was, these oddities came to Joe Dawson's attention, and he relayed his concerns to Macleod. When Duncan learned that Horton was alive and that Joe was responsible, he was furious. Several attacks on several fronts followed, with ambushes well-staged at both Duncan's dojo-loft and even when he went after the killers. With the aid of his mortal friend Charlie De Salvo and a police agent, Duncan was finally able to separate the fractious allies, beheading St. Cloud. Horton was apparently shot by Joe and fell into the Seine while trying to flee on a boat in Paris. During several occasions in this battle, Horton taunted Macleod with his survival, proclaiming himself the man Duncan couldn't kill.

Horton's final scheme while living went straight to the heart of his nemesis. Recruiting a wanted killer by the name of Lisa Halle, he paid her to subject herself to plastic surgery and acting lessons, emerging as the perfect duplicate of the late Tessa Noel. Going one step further, he took one of his agents and had him befriend Richie Ryan, who kept on with the friendship despite some red flags raised by Macleod. Horton, as he had in times past, sacrificed this pawn in such a way as to create a rift between Duncan and his protege. Horton then staged Macleod's sightings and 'accidental' meeting with the remade Lisa, his love for Tessa overcoming what he knew in his heart had to be a lie. Even the briefly bitter Richie calmed down when he saw her, now realizing that Macleod had been correct to be suspicious. A surgery scar gave Lisa away, and Duncan played through their trap to see it done. Once more, Horton killed his pawn, with a dying Lisa wishing she really could have been Tessa for him. This time, though, Joe and Richie blocked Horton's escape routes, and Duncan, taunting Horton back with his famous 'unkillable' boast, put the lie to it and this time made certain he was done for.

Joe had Horton buried nearby in Paris, as his daughter back home in Seacouver still had not forgiven him killing the man she loved. Horton's life was done with, but by action and by specter he would not stop haunting the lives of those who had known him. In fact, one of his earliest Immortal killings would come back at both Watcher and Immortal.

The couple mentioned previously were Jacob and Irena Galati, two Immortals adopted by Romany clans in Eastern Europe. Jacob had a long history of not tolerating slights, wrongs and crimes done against the Romany, and in particular against Irena, often going to very violent methods of fighting back. When Irena fell by Horton's hands some months before Darius, he used the power from her Quickening to escape, grief-stricken and swearing vengeance. Knowing now that there were those who watched his kind, Galati stalked Watchers all over the world, learning what he could of them, never realizing their main purpose was benign, and that he and his wife had been targeted by radicals, most of them now dead thanks to their old friend Duncan Macleod. The Watchers' Council came to the conclusion that all their troubles had started when Joe Dawson revealed their existence to Macleod, almost willfully ignoring every other instance of rogue Watchers, most especially Horton. When Galati killed the son of Council leader Jack Shapiro, Joe was sentenced to death and Macleod went on the run, looking for whoever was doing the killing. With both combatants driven insane by grief, Macleod, Methos and Dawson watched as the Watchers almost became an entirely Hunter-like organization, till Shapiro's killing of Galati and Shapiro's subsequent breakdown finally put Joe in charge. Yet many trained Watchers had died, and presumably some Immortals who had nothing to do with the feud.

It is worth noting that, in the flashbacks with his character, a beast's roar was heard as a sound effect when Horton killed Irena Galati. The same sound effect was heard in scenes that same season with Kronos and Roland Kantos, and then as the sound effect of  the enemy in the dark arc that closed Season 5, with Horton again showing up, albeit in a different way.

Without warning, Duncan Macleod seemed to become badly mentally ill. He began to see, among others known to be dead, Horton and Kronos alive and taunting. Learning that Joe Dawson was sending Horton's body back to his daughter, Macleod, recalling that Joe had aided his fallen brother-in-law in the past, demanded to see the body and went so far as to pry open his coffin. All he found was the skeletal remains of a man some years dead.

At first, he and his friends thought that the pressures of a heroic Immortal's life had weighed down upon him too hard. But then he learned of a prophecy apparently placing himself as a Champion Of Light against a millenial demon, Ahriman. This did not shore up his standing with his friends, and Duncan began to seem a danger to them, to himself and perhaps even to keeping the existence of Immortals a a secret. But whatever it truly was, Ahriman was real, and pushed Macleod's sanity to the brink. In an illusory swordfight, he faced Horton, Kronos and the illusion of Richie Ryan. When the real Richie came to aid him, Macleod, who could no longer tell what was real and what was not, beheaded his protege. Shattered, he withdrew and vanished for an entire year, to gird himself for the fight against Ahriman. Several times during his struggles with the entity, it again appeared as Horton, till Duncan refused to see evil as something outside himself, but accepted that it was within all of us, just as was good. One of the last sights Duncan saw as the apocalyptic vision quest concluded was Horton' s image vanishing and being replaced by his body in the coffin. It was never learned if, in life, either Horton or Kronos had any affiliation with Ahriman. But again, this was not the last time Duncan would see Horton.

A Duncan utterly wearied by his losses faced his limit when yet another long-term vengeance seeker once more kidnapped all those close to him, with only Methos stepping in and stopping him from merely surrendering himself as demanded by the foe. During a rescue attempt, Macleod was shot, and while dead, had a vision of once again seeing his old friend Hugh Fitzcairn (a casualty of the schemes of evil Immortal Kalas), who claimed to be an angel now. In a very familiar plot, 'Fitz' showed Macleod his true worth in a world where he had never been born. Needless to say, one of the chief beneficiaries of Macleod's absence from history was James Horton, who had risen to control the Watchers and corrupt the entire organization to his bigoted mission. Not only had he driven a broken Joe Dawson out and onto the streets, he kept up his habit from the main timeline of killing his pawns. One of these was the mortal lover of Methos, who outed him believing that Horton meant no harm. Even worse, Methos was rescued by Kronos, and eventually corrupted by him once again, with the two set to match Horton's crusade with renewed terror on a Bronze Age scale for the modern world. Richie Ryan was mentored by this pair, and killed by them when he refused to kill Joe Dawson, which Methos then did himself. For his part, Horton had a clear field to kill every Immortal he could find, including Amanda. Before the vision ended, Fitz indicated that the war between the Hunters and the Horsemen could easily consume the whole world.

For once, Horton and Kronos did Macleod a favor. Seeing their supreme victories in his vision reminded him of what he fought against, and the enemy who likely would have always been an easy victory for Macleod in normal times, became so.

In the feature film Highlander : Endgame, a secretive group of Watchers kept Immortals alive but in stasis in a fortress called The Sanctuary, reasoning that, if they were not available to fight and be killed, the Prize would never be realized. While their goals were at least similar to Horton's, and their means of recruiting and keeping Immortals for this place questionable, it is unknown whether they had any connection with, or were inspired by, Horton's bloody crusade.