Before it became a long-running original television show, Fantasy Island was introduced to viewers in 1977 through two highly-rated made-for-television films in which Mr. Roarke and Tattoo played relatively minor roles. Airing from 1978 to 1984, the original series starred Ricardo Montalbán as Mr. Roarke, the enigmatic overseer of a mysterious island somewhere in the Pacific Ocean, where people from all walks of life could come and live out their fantasies, albeit for a price.

Roarke was known for his white suit and cultured demeanor, and was initially accompanied by an energetic sidekick, Tattoo, played by Hervé Villechaize. Tattoo would run up the main bell tower to ring the bell and shout "The plane! The plane!" to announce the arrival of a new set of guests at the beginning of each episode. This line, shown at the beginning of the show's credits, became an unlikely catch phrase because of Villechaize's spirited delivery and French accent (he actually pronounced it, "Ze plane! Ze plane!"). In later seasons, he would arrive in his personal go-kart, sized for him, and recklessly driven to join Roarke for the visitor reception while staff scrambled to get out of his way. From 1980 to 1982, Wendy Schaal joined the cast as another assistant named Julie. In a highly unpopular move with both fans and the cast, the producers fired Villechaize from the series before the 1983–1984 season (which ended up being its last) and Tattoo was replaced by a more sedate butler type named Lawrence, played by Christopher Hewett. Lawrence's personality was exactly the opposite of Tattoo's in many ways. For instance, Lawrence was also responsible for the bell ringing, but instead of climbing to the tower he simply pushed a button outside to have the bell ring automatically.

A Grumman Widgeon aircraft was used for the series. As each visitor exited the plane Roarke would describe to Tattoo (or another assistant) the nature of their fantasy, usually with a cryptic comment suggesting the person's fantasy will not turn out as they expected. Roarke would then welcome his guests by lifting his glass and saying: "My dear guests, I am Mr. Roarke, your host. Welcome to Fantasy Island." This toast was usually followed with a warm smile but sometimes (depending on the nature of a guest or their fantasy) his eyes would show concern or worry for a guest's safety.

Roarke's personal vehicle was an orange Dodge Aspen station wagon with a Safari top with the stance of a modern-day sport utility vehicle.

Very little is known about the man known as Mr. Roarke and it isn't clear if that's his first, last, or only name. Although most guests know him as "Mr." Roarke, many people close to him, including past lovers, have referred to him only as "Roarke", which suggests he may not have any other names. He is the sole owner and proprietor of Fantasy Island.

Roarke's actual age is a complete mystery. In the pilot movie, he comments how the guests who come to his island are "so mortal" and there are hints throughout the series that suggest Roarke may be immortal. In "Elizabeth", a woman from Roarke's past appears, but it's revealed that she died over three hundred years ago. Another episode even suggests that he was once intimate with Cleopatra. However old he is, Roarke has come to know many seemingly-immortal beings over his time on Earth, including ghosts ("The Ghost's Story"), a genie ("A Genie Named Joe"), the mermaid Nyah ("The Mermaid", "The Mermaid Returns", "The Mermaid and the Matchmaker"), the goddess Aphrodite ("Aphrodite"), and even Michael, the Angel of Death ("The Angel's Triangle"). In two episodes ("The Devil and Mandy Breems", "The Devil and Mr. Roarke"), Roarke even faces The Devil (played by Roddy McDowall), who has come to the island to challenge him for either a guest's immortal soul or his. It is mentioned this is not the first time they have confronted each other and Mr. Roarke has always been the winner. In the second story, the Devil himself was one of the island's guests, claiming he was only there to relax and had no interest in Roarke's soul at the time. However, this turned out to be yet another ruse.

Roarke had a strong moral code, but he was always merciful. He usually tried to teach his guests important life lessons through the medium of their fantasies, frequently in a manner that exposes the errors of their ways, and on occasions when the island hosted terminally ill guests he would allow them to live out one last wish. Roarke's fantasies were not without peril, but the greatest danger usually came from the guests themselves; in some cases people actually got themselves killed due to their own negligence, aggression or arrogance. When necessary, Roarke would directly intervene when the fantasy became dangerous to the guest. For instance, when Tattoo was given his own fantasy as a birthday gift, which ended up with him being chased by hostile natives in canoes, Mr. Roarke suddenly appeared in a motorboat, snared Tattoo's canoe with a grappling hook and towed it away at high speed to help his employee escape. With only a few exceptions, Roarke always made it quite clear that he was powerless to stop a fantasy once it had begun and that guests must play them out to their conclusion.

In the pilot movie, Roarke was actually a rather sinister figure, but once the series went into production he was depicted as more benevolent.

In later seasons, there were often supernatural overtones. Roarke also seemed to have his own supernatural powers of some sort (called the "Gift of the McNabs" in "Delphine"), although it was never explained how this came to be. In one episode, when a guest says "Thank God things worked out well", Roarke and Tattoo share a very odd look and Roarke says in a cryptic way "Thank God, indeed". In the same episode, Roarke uses some mysterious powers to help Tattoo with his magic act.

The usual format of each episode consisted of an introduction in which Roarke would describe to Tattoo (or another assistant) the nature of each person's fantasy, usually with a cryptic comment suggesting the person's fantasy will not turn out as they expected. The episode would then alternate between two or three independent story lines as the guests experienced their fantasies and interacted with Roarke. Often, the fantasies would turn out to be morality lessons for the guests (for example, one featured a man who clamored for the "good old days" to be taken back to the Salem witch trials), sometimes to the point of (apparently) putting their lives at risk, only to have Roarke step in at the last minute and reveal the deception. It is mentioned a few times that a condition of visiting Fantasy Island is that guests never reveal what goes on there. A small number of guests decided to make the irrevocable choice to stay permanently, living out their fantasy until death; one such person was an actor who had been in a Tarzan-type television series in the 1960s. Aside from a "clip show" ("Remember...When?") the only episode with a single storyline was "The Wedding", in which terminally-ill Helena Marsh returned to Fantasy Island to spend her last days as Roarke's wife.