For this theory, a look at the soundtrack of “The Lord of the Rings: The Rings of Power” helps. Observant viewers, and even more observant listeners, will notice that whenever The Stranger appears, the same music called “Wise One” on the soundtrack plays. And in the Quenya language invented by ‘Lord of the Rings’ creator JRR Tolkien, the word ‘Istari’ actually means ‘the Wise’ (or ‘Wise Ones’), i.e. ‘Wise One’.
In addition, the stranger shows a special ability: He can communicate with fireflies. And so far only one character in the whole “Lord of the Rings” cosmos has been able to do that: Gandalf. It’s not entirely clear whether other Istari can do this, so it’s also possible that the stranger might be Saruman or Radagast, the other well-known Istari characters.
Should the creators really install one of the Istari here, it would be a huge change from Tolkien’s works: In his templates, the Istari are first sent to Middle-earth, many years after the time in which “The Rings of Power” takes place.