All that we know about Damis comes from Apollonius' biographer Philostratus who wrote his Life of Apollonius of Tyana between 217 and 238. Some scholars[who?] believe the notebooks of Damis are an invention of Philostratus, others think it was a real book forged by someone else and used by Philostratus. And some scholars think that Damis never existed at all. F.C. Conybeare, however, points out the extreme and unnecessary sceptism of this theory.
E. Rabinovitch even advocates a high probability of the real existence of Damis' notebooks. It is possible that Philostratus did use a biography of Apollonius by Damis, who was however, not trustworthy (that is, he was like the so-called aretalogi, sought to embellish the life of his master).
According to Philostratus, Apollonius met Damis in a city which Philostratus calls "Old Ninos", which from its location cannot be Nineveh, but is in fact the "holy city" of Hierapolis Bambyce (Manbij) in Syria. Damis admired Apollonius so much that he became his disciple, and kept a record of Apollonius' actions and sayings, the so-called Memoirs (or Diary) of Damis. These notes came into the possession of the empress Julia Domna, and it was she who commissioned Philostratus to write a biography of Apollonius, the extant Life of Apollonius of Tyana. That's what Philostratus asserts.