Trained in combat, survival, and sword-fighting by his elder cousin Connor (the original hero of the Highlander movie franchise) and others, Duncan travels the world in search of friendship and adventure, helping people when he can, sometimes fighting alongside or against other immortals.

Rather than ignore the original story entirely, the series is set in a new timeline where the events of the film occurred, but Connor's final battle did not earn him The Prize because many immortals were still alive on Earth.

After he was cast, actor Adrian Paul suggested his character should be a new immortal Scottish Highlander, to avoid critical comparisons with the original film and Lambert's performance.

[3] As a child, Duncan hears stories about Connor MacLeod, a man who had died in battle in 1536 only to revive later, fully healed, which led the clan to banish him for witchcraft.

Connor finally finds Duncan in 1625, having heard stories that another member of the Clan MacLeod was exiled for unnatural powers.

[6] Connor befriends Duncan and teaches him his true nature, explaining there are rare people born with a power that, along with making them unable to produce children, activates if they suffer the shock of violent death.

Connor explains that other immortals can take Duncan's Quickening [definition needed] if they kill him, absorbing his knowledge and power.

[2] Preferring friendship, art, and the exchange of knowledge to violence and killing, Duncan travels the world and becomes an ally of other immortals if they don't challenge him.

Originally taking pride in being reckless and a little uneducated, he matures into a worldly person, becoming knowledgeable in many fields and martial arts, and learning many languages.

"[12] In America, Duncan lives with the Sioux people, taking a lover named Little Deer and helping raise her child Kahani, whom he loves as his own.

When the tribe is later murdered by white colonials and a bigoted immortal named Kern, Duncan temporarily leaves society and the Game by living in isolation on holy ground.

Richie is hired to work at the antique shop and becomes a younger brother of sorts to Duncan and Tessa, adding enthusiasm and comic relief to their adventures.

MacLeod later learns that there is a group of mortals who have been secretly documenting the lives and actions of immortals for thousands of years—an organization called The Watchers.

While most are benevolent and don't interfere, a sub-group called the Hunters goes rogue, hunting down immortals so that none of them who win the Prize may use that power to rule humanity.

Meanwhile, Joe Dawson, a Watcher assigned to observe Duncan, attempts to forge a friendship with the Highlander and openly aids him at times.

When Richie repeatedly seems motivated by emotion rather than reason in his battles, Duncan decides he has taught the young man enough and they must follow different paths now.

Soon afterward, Anne witnesses Duncan apparently dying and he decides to keep his survival secret to protect her, leaving for Paris once more.

During this visit, Duncan uses his old clan broadsword to avenge the death of his father, realizing the man was killed by a Viking immortal.

When a demonic entity warps his perception with hallucinations and drives him to attack a beloved friend,[20] he spends a year in isolation to process the trauma and his guilt.

In the two-part series' finale episodes, "To Be" and "Not To Be," Duncan has visions of a world where he was never born and realizes the positive effect he has had on many people, even Richie and Tessa.

While Connor advises that Kate be allowed to simply age and die naturally, Duncan decides to activate her immortality by giving her a fatal stab wound.

"[22] Continuing Duncan's adventures several years after Highlander: Endgame, the story takes place in a possible future version of Earth where human society has fallen into chaos.

Written by series producer David Abramowitz and directed by Don Paonessa, the film does not acknowledge the events of Highlander: The Source.

A series of nine licensed novels were released from October 1995 to February 1999: The Element of Fire, Scimitar, Scotland the Brave, Measure of a Man, The Path, Zealot, Shadow of Obsession, The Captive Soul, White Silence, and An Evening at Joe's.

The books depict an alternate continuity where Tessa did not die at the end of the episode "The Darkness" and explores Duncan's life afterward.

In another story, collected as Highlander: Armageddon, Duncan is captured by a renegade Watcher group called the Eye and forced to compete in a fight club against other immortal warriors.

Adrian Paul auditioned and was cast but then suggested that since Lambert's portrayal of Connor was popular with fans it would be better to create a new character rather than try to replace him.

The production agreed this would allow the show more freedom to create its own hero, so it was decided that Adrian Paul would now be playing Connor's student and kinsman Duncan MacLeod.

Connor had been portrayed in the films as someone who had a good sense of humor and cared deeply for some people, but was largely introverted and tried to live quietly without drawing much attention to himself.

With a strong sense of honor and a sometimes stubborn determination to protect and avenge his friends, he is sometimes called a Boy Scout or compared to a superhero by other characters.