Ultima Trilogy I,II & III

In Ultima I: The First Age of Darkness (1981), 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. Minax launches an attack on the Stranger's homeworld of Earth. Her actions cause doorways to open to various times and locations throughout Earth's history, and brings forth legions of monsters to all of them. The Stranger, after obtaining the Quicksword that alone can harm her, locates the evil sorceress at Castle Shadowguard at the origin of time and defeats her.

Ultima III: Exodus (1983) reveals that Mondain and Minax had an offspring, the eponymous Exodus, "neither human, nor machine", according to the later games (it is depicted as a computer at the conclusion of the game, and it appears to be a demonic, self-aware artificial intelligence). 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.