Alhaitham is the reincarnation of King Deshret, therefore they have similar looks and personality. Alhaitham/King Deshret is a scholar who is fueled by a desire to understand the underlying principles of the world around him. He greatly values the pursuit of knowledge and dislikes meaningless noise and matters that distract or divert him from his chosen pursuits. The King doesn’t recognize Kaveh, because it’s a different time where he’s still The King.