Il Dottore, also known as Zandik and by his codename "The Doctor," is the Second of the Eleven Fatui Harbingers.
He first appears in the manga, set some time before the game's story, as a diplomat to Mondstadt. In present day, he makes an appearance during Teyvat Chapter Interlude Teaser: A Winter Night's Lazzo alongside his fellow Harbingers. He makes his in-game debut (in his Omega Build) during Archon Quest Chapter III, Act III, where he is revealed to be working with the sages of Sumeru.