In Ultima I: The First Age of Darkness (1980), the Stranger is first summoned to Sosaria to defeat the evil wizard Mondain who aims to enslave it. Since Mondain possesses the Gem of Immortality, which makes him invulnerable, the Stranger locates a time machine, travels back in time to kill Mondain before he creates the Gem, and shatters the incomplete artifact. Ultima II: The Revenge of the Enchantress (1982) details Mondain's secret student and lover Minax's attempt to avenge him. Having destroyed Earth, Minax launches the conquest of Sosaria but the Stranger escapes Earth in time, pursues the evil sorceress to the Castle Shadowguard at the Origin of Time and defeats her. Ultima III: Exodus (1983) reveals that Mondain and Minax had an offspring, the titular Exodus, "neither human, nor machine", according to the later games. Some time after Minax's death, Exodus starts his own attack on Sosaria and the Stranger is summoned once again to destroy it. Exodus was the first installment of the series featuring a player party system, which was used in many later games.
Ultima IV: Quest of the Avatar (1985) marked a turning point in the series from the traditional "hero vs. villain" plots, instead introducing a complex alignment system based upon the Eight Virtues. Although Britannia now prospers under Lord British's rule, he fears for his subjects' spiritual well-being and summons the Stranger again to become a spiritual leader of Britannian people by example. Throughout the game, the Stranger's actions determine how close he comes to the ideal and upon achieving enlightenment in every Virtue, he becomes their "Avatar". In Ultima V: Warriors of Destiny (1988), Avatar returns to Britannia to find that after Lord British had been lost in the Underworld, his throne was usurped by Lord Blackthorn who enforces a radically twisted vision of the Virtues, deviating considerably from their original meaning. Avatar and his companions overthrow the tyrant and restore the Virtues in their true form. Ultima VI: The False Prophet (1990) details the invasion of Britannia by Gargoyles, which Avatar and his companions have to repel, and explores the themes of racism and xenophobia.
The spin-off Worlds of Ultima series uses the game engine of Ultima VI and describes Avatar's adventures after its conclusion. In Worlds of Ultima: The Savage Empire (1990), a failed experiment transports Avatar to the Valley of Eodon, a jungle world populated by thirteen primitive tribes whom he unites against a common enemy, the insectoid Myrmidex. Ultima: Worlds of Adventure 2: Martian Dreams (1991) takes place after The Savage Empire and sees Avatar travel back in time to the Victorian era and eventually land on Mars to rescue humans stranded on it by accident and to restore the native Martian civilization. The third game, Ultima: Worlds of Adventure 3: Arthurian Legends was planned to be set in the times of King Arthur but was canceled in 1993.
Ultima VII consists of two games: Ultima VII: The Black Gate (1992) and Ultima VII, Part Two: Serpent Isle (1993), with an expansion pack released for each (Forge of Virtue and The Silver Seed, respectively). In The Black Gate, Avatar is entangled in the plan of a seemingly virtuous organization named the Fellowship to create a gateway for the evil entity known as the Guardian to enter Britannia. Following the Fellowship's defeat, its founder Batlin flees to the Serpent Isle, the remnant of a lost Sosarian continent, and is pursued by Avatar and companions in Part Two. By the end of the game, Avatar confronts the Guardian but is overpowered and thrown into another world, where Ultima VIII: Pagan (1994) is set. In Pagan, Avatar masters the ways of Elemental Titans, god-like servants of the Guardian now controlling that world, defeats them with their own magic, and finally returns to Britannia. An expansion pack, The Lost Vale, was canceled after Ultima VIII failed to meet sales expectations. The final installment of the series, Ultima IX: Ascension (1999) sees Britannia conquered and its Virtues corrupted by the Guardian, so Avatar has to cleanse and restore them. The Guardian is revealed to be the evil part of Avatar himself, expelled from him when he became the Avatar. To stop it, he has to merge with it, destroying himself as a separate entity. The unreleased version of the plot featured a more apocalyptic ending, with the Guardian and Lord British killed, Britannia destroyed, and Avatar ascending to a higher plane of existence.
The second spin-off series, Ultima Underworld, consisted of two games. Set after Ultima VI, Ultima Underworld: The Stygian Abyss (1992) sees Avatar descending into the Great Stygian Abyss to rescue a Britannian baron's kidnapped daughter and prevent the summoning of a powerful demon. Ultima Underworld II: Labyrinth of Worlds (1993) is set between the two parts of Ultima VII and starts with the Guardian trapping Lord British, Avatar and his companions within impenetrable barrier in their castle. To free them, Avatar has to travel through several parallel universes looking for a way to undo the spell.
Ultima Online (1997), a MMORPG spin-off of the main series, has become an unexpected hit, making it one of the earliest and longest running successful MMORPGs of all time. Its lore retconned the ending of Ultima I, stating that when the Stranger shattered the Gem of Immortality, he discovered that it was tied to the world itself, therefore its shards each contained a miniature version of Britannia. The player characters in Ultima Online exist on these "shards". Seven expansion packs for UO have been released (The Second Age, Renaissance, Third Dawn, Lord Blackthorn's Revenge, Age of Shadows, Samurai Empire, and Mondain's Legacy), with the eighth (Stygian Abyss) currently in development. The aging UO graphic engine was renewed in 2007 with the official Kingdom Reborn client. Ultima Online 2, later renamed to Ultima Worlds Online: Origin and canceled in 2001, would have introduced steampunk elements to the game world, following Lord British's unsuccessful attempt to merge past, present, and future shards together.
The canceled MMORPG Ultima X: Odyssey (2004) would have continued the story of Ultima IX. Now merged with the Guardian, Avatar creates a world of Alucinor inside his mind, where the players were supposed to pursue the Eight Virtues in order to strengthen him and weaken the Guardian. Ultima X was developed without participation of the original creator Richard Garriott and he no longer owns the rights to the series. However, he still owns the rights to several of the game characters so it is impossible for either him or Electronic Arts to produce a new Ultima title without getting permission from each other.
Ultima game boxes often contained so-called "feelies"; i.e. from Ultima II on, every game in the main series came with a cloth map of the game world. Because the maps were crucial to navigation in the Ultima game, they also served as anti-software piracy devices, since the primitive file sharing methods of the 1980s did not allow transferring large images over the early low-baud rate computer connections used by darknets. Furthermore, the map was large (18" x 12") and in color, and so was not easily reproduced by photocopiers. Starting with Ultima IV, small trinkets like pendants, coins and magic stones were found in the boxes. Made of metal or glass, they usually represented an important object also found within the game itself. These other feelies served a similar purpose, being crucial elements of the gameplay not otherwise represented in the game itself, and it was almost impossible to transfer their images over phone lines or by the low capacity floppy disks of the time.
Along with Ultima's I-VIII this collection also included:
UO spawned two sequel efforts that were cancelled before release: Ultima Worlds Online: Origin (cancelled in 2001, though the game's storyline was published in the Technocrat War trilogy.) and Ultima X: Odyssey (cancelled in 2004). However, several expansions were released for Ultima Online, adding new features and areas to be explored. They are The Second Age, Renaissance, Third Dawn, Lord Blackthorn's Revenge, Age of Shadows, Samurai Empire, and Mondain's Legacy.
It was founded on Prodigy in 1992 as a "help club" to assist members and guests on completing the games in the series. It also became a social club where members shared tips and special tricks to take advantage of "easter eggs" built into the game. Changes to Prodigy's rate system and the expansion of the Internet caused the group to leave Prodigy.