In this article first of all we invest the name of Therita in Avesta and then the frequency of this name in middle Persian texts, after that introduce the first doctor in the historical books of Islamic Iran that some of them say he is Fereidoon and some say he is Jamshid. These three Iranian mythical characters somehow have connections with medicine, and in order to define the first doctor all three should be studied and differences in their characteristics in sources should be noticed.
By a way it is thought that Ferdosi, in first four verses of Jamshid's introduction describes Therita adjectives for Jamshid.
