There are nine installments in the main series which are divided into three trilogies: The Age of Darkness, Enlightenment and Armageddon.
The Age of Darkness
| The protagonist, known as " The Stranger", is summoned by Lord British and must seek and destroy the Gem of Immortality before the entire population of Sosaria become enslaved by the evil wizard Mondain. Because Mondain is in possession of the gem, he is invincible and therefore impossible to defeat. In order to save the kingdom, The Stranger must travel back in time and kill Mondain before he completes the gem.|
| After years of resentment for the death of her mentor and lover, Mondain, Sorceress Minax sets out to seek revenge on the Stranger. The sorceress travels to the Time of Legends, where she releases her minions to different time eras and manipulates the mind of men, which almost resulted in the destruction of humankind. The Stranger is once again summoned by Lord British and must put a stop to Minax's evil plans by manipulating time gates and following Minax to the Age of Legends.|
| Sosaria is once again under attack; but this time by Exodus, an evil entity created by Mondain and Minax before their demise. Lord British summons The Stranger to track down Exodus and put an end to its rampage.|
The Age of Enlightenment
| After the demise of Mordain, Minax, and Exodus, Sosaria experienced many changes, some continents were lost while others were created, cities were rebuilt, and life came back to normal. With all these changes, Lord British, now ruler of Sosaria renamed the kingdom Britannia. This peace soon became a concern to the lord as he feared for the spiritual well-being of the people. Lord British then set up the Quest of the Avatar, where he would need someone to come forth and become a spiritual role-model for people to follow. Through moral choices, the protagonist would learn about the eight virtues and ultimately receive the Codex of Ultimate Wisdom and become the Avatar.|
| Lord British is lost in the Underworld and Lord Blackthorn, with the help of three mysterious henchmen known as the Shadowlords, seize the throne and immediately begins to rule Britannia with an iron fist. Unable to yield before the tyrant, a group of townsmen summon the Avatar by using a magic coin. The Avatar then journeys with his companions, the Warriors of Destiny, to defeat Lord Blackthorn, his henchmen, and to reinstate Lord British to the throne of Britannia.|
| The Avatar was captured by gargoyles, but as he was about to be sacrificed, he was rescued by the Warriors of Destiny. However, once the Warriors returned to Britannia, they realized that the gargoyles had captured the shrines of Virtue. In order to save Britannia from the gargoyles, the Avatar sets on a quest to rescue them.|
The Age of Armageddon
| After 200 years, the Avatar returns to Trinsic, Britannia via a Red Moongate, a device used to travel long distances quickly at night. Upon his arrival, the Avatar is given the task of investigating a grisly ritualistic murder. After speaking to the locals, the Avatar learns of a religious group known as the Fellowship and is encouraged by many, including Lord British, to join the group. As the investigation progresses, the Avatar discovers that the Fellowship is more than what it seems to be.|
| With the destruction of the Black Moongate, which prevented the evil entity known only as The Guardian from entering Britannia, Batlin flees to Serpent Isle, but was soon discovered and defeated by the Avatar.|
| After the defeat of Batlin, The Guardian exiles the Avatar to the unruly world of Pagan. In order to return to Britannia, the Avatar must defeat the four Titans in Pagan; each of the Titans has mastery in an elemental domain: Earth, Air, Water, and Fire. In order to defeat the Titans and return to Britannia, the Avatar must seek mastery of these elements and reconstruct the black stone gate the Guardian used to exile him to Pagan.|
| After defeating the Titans, the Avatar returns to Britannia, which has been taken over by The Guardian, and Lord Blackthorn now sits on the throne of Lord British. The landscape of Britannia has also been changed by the appearance of columns that have nefarious effects on the inhabitants. The Avatar learns that the columns were created by the corruption of the shrines of Virtue that were stolen in Ultima VI and must be cleansed in order to reverse the effects. In the final showdown between the Avatar and the Guardian, it was revealed that the Guardian is the dark side of the Avatar and the only way for the Avatar to defeat the Guardian and to save Britannia was to ascend to a higher plane while taking the Guardian along with him.|
Subseries and Spinoffs
Aside from the core series, Ultima has spawned a number of peripheral games. The Worlds of Ultima series featured side stories about the Avatar traveling to other worlds. The two Ultima Underworld games were groundbreaking first-person titles that paved the way for System Shock, a later Origin-published game that was highly influential.
In 1997, Ultima Online launched, becoming one of the first MMORPGs to achieve popular success. The game has had numerous expansions and is still running today.