Don Quixote’s real first name before he renames himself is Alonso.
Miguel de Cervantes eventually identifies him as Alonso Quijano, a hidalgo, or minor gentleman, from La Mancha. After reading so many tales of chivalry that his judgment becomes distorted, he decides to revive knight-errantry and adopts the grand name Don Quixote de la Mancha.
The name is slightly complicated by Cervantes’s playful narration. Early in Part One, the narrator jokes that the character’s surname may have been Quijada, Quesada, or Quijana. The definitive form, Alonso Quijano, is disclosed only near the end of Part Two. That delayed revelation is part of the novel’s mock-scholarly style and its recurring uncertainty about documents and authors.
A common mix-up is to treat Don Quixote as his birth name. It is instead his self-created knightly identity; Alonso is the personal name behind it. Sancho Panza continues to call him Don Quixote during their adventures, while the character’s return to Alonso Quijano signals his recovery of sanity near the novel’s conclusion.