"Ultima is a series of fantasy computer role-playing games from Origin Systems, Inc. Ultima was created by Richard Garriott, a.k.a. Lord British. Several games of the series are considered seminal games of their genre. Today, Electronic Arts holds the brand.
The main Ultima series consists of nine installments (the seventh is further divided into two parts) which are grouped into trilogies or "Ages": The Age of Darkness (Ultima I-III), The Age of Enlightenment (Ultima IV-VI), and The Age of Armageddon (Ultima VII-IX), also referred to as "The Guardian Saga" after its chief antagonist. The first three games were set in a fantasy world named Sosaria but during the cataclysmic events of The Age of Darkness, three quarters of it vanish. What is left becomes known as Britannia, a realm ruled by the benevolent Lord British where the later games mostly take place. The protagonist of all games is a canonically male resident of Earth who is called upon by Lord British to protect Sosaria and later, Britannia from various dangers. Originally, the player character was referred as "the Stranger" in the games but by the end of Ultima IV, he becomes universally known as the Avatar."
Source: Wikipedia, "Ultima_(series)", available under the CC-BY-SA License.