Short answers, pulled from the story.
The first Assassin's Creed game was released in November 2007. This title fundamentally altered the trajectory of the video game industry through its narrative structure rather than its graphics or combat.
Ubisoft Montreal developed the original Assassin's Creed game under the leadership of Patrice Désilets, Jade Raymond, and Corey May. The developers drew heavy inspiration from the 1938 novel Alamut by Vladimir Bartol to fictionalize the historical Hashashin sect of medieval Iran.
The Animus is a device that allows users to relive the memories of their ancestors through their genetic material. This technology was developed by the Templar-controlled mega-corporation Abstergo Industries and serves as the diegetic interface for the player.
Desmond Miles is a bartender and former Assassin who is forced to explore the memories of his ancestors to prevent a catastrophic solar flare. He ultimately activates the global aurora borealis device in the Grand Temple to block the flare at the cost of his own life.
Ezio Auditore da Firenze is a young nobleman from Florence who becomes an Assassin after his father and brothers are killed by the Templars. His journey takes him through the Italian Renaissance where he makes allies such as Leonardo da Vinci and combats enemies such as the Pazzi family and Rodrigo Borgia.