The modern-day protagonist in the original Assassin's Creed is Desmond Miles.
Desmond is a former Assassin who has hidden from the Brotherhood and works as a bartender before being abducted by Abstergo Industries. Abstergo forces him to use the Animus, a machine that lets a person experience ancestral genetic memories, so its researchers can search for information about a Piece of Eden.
Through the Animus, Desmond experiences the memories of Altaïr Ibn-La'Ahad, the Assassin at the center of the historical storyline. The modern-day sections frame the historical missions and establish the series' recurring conflict between Abstergo, the Templars' corporate front, and the Assassins.
Desmond's surname is sometimes confused with William Miles, his father and a senior Assassin. Warren Vidic is an Abstergo scientist who supervises the experiment, while Clay Kaczmarek is another subject associated with the Animus. Those characters are important, but Desmond is the original game's modern-day lead.