Name and designation. Marcus in 01-12 calls him simply Ἀλέξανδρος ὁ Πλατωνικός — "Alexander the Platonist," without indication of origin, without a city-epithet. This is significant: for all the other teachers of Book I, Marcus either gives a school-label (Stoic, Platonist) or names them without a school-label but never leaves them in such complete anonymity as to where the teacher worked and where Marcus met him. Alexander the Platonist is the most "attribute-less" teacher in the catalogue, and this in itself creates the problem of identification.

The problem of the identification with Alexander Peloplaton. The standard popular identification — reflected in Rogovin's footnote to 01-12 and going back to a classical commentatorial consensus of the nineteenth century — is: Marcus's "Alexander the Platonist" = Alexander Peloplaton of Seleucia, the well-known Second Sophistic figure portrayed by Philostratus in Vitae Sophistarum (the second book — in which Philostratus treats the sophists of the second century). Peloplaton — a brilliant, travelling orator nicknamed "Peloplaton" (from πηλός — "clay," "mud"; the explanations vary: either "Plato of clay," i.e. an imitator, or "the clay Plato," a Plato-figurine baked of imitation) — served Marcus as ab epistulis Graecis, i.e. secretary for Greek correspondence, during the Eastern (Parthian) campaign of 161–166.

This identification is contested. The main objections (see Brunt in his classic article on Marcus's Meditations, JRS 1974; Birley in his biography of Marcus, ch. 3 "Education"):

1. Chronology. Peloplaton enters Marcus's circle as a secretary — that is, in the established service-status of a mature man, not as the teacher of the young Marcus. Marcus in Book I gives thanks for formative teaching, not for late administrative contact.
2. Generic position. Peloplaton is a sophist, a rhetor, a virtuoso of public declamation; Marcus thanks a teacher of philosophy (a Platonist) for an ethical-practical discipline. These are different generic positions in the Antonine intellectual geography.
3. The silence of Philostratus. If Marcus's Alexander the Platonist is Peloplaton, it is strange that Philostratus — in whom Alexander Peloplaton has a developed portrait — does not once give the tutorial role to Marcus as a biographical fact; he emphasises only the secretarial service.

The cautious modern consensus (Hadot, Birley, Hard): the identification is not proved, but also not refuted; Marcus's Alexander the Platonist may have been a separate figure that has not survived in our prosopography. The biographical sketch below is set out in conditional mode — "if the identification is correct, then…" — with the hypothetical status made explicit.

Conditional biography (on the identification with Peloplaton). Alexander was probably born in the early second century at Seleucia in Cilicia (south-eastern Asia Minor) — a city with an established Greek school-tradition. He received a rhetorical education and, on Philostratus's report, studied among others with Dionysius of Miletus, a first-generation figure of the Second Sophistic. His active career was a travelling one: Alexander performed at Athens, in the capitals of the Asian Minor provinces, and (per Philostratus) was summoned to Rome in the 160s for service with Marcus during the Eastern campaign. The nickname "Peloplaton" is recorded as current in his time and preserved by Philostratus. On the general tone of Philostratus's portrait — a figure of high professionalism but of disputed ethical valuation (the characteristic Philostratean division: great masters of speech, not necessarily great moral exemplars).

What Marcus confirms in any case. Regardless of the verdict on identification, Marcus in 01-12 records two internal facts about his Alexander:

1. He is a Platonist (Πλατωνικός) — a representative of the Platonic tradition, not the Stoic one. In Book I this is the only explicit attribution of a Platonist.
2. He is a teacher who transmitted to Marcus not a doctrinal thesis but an ethical-practical discipline — a specific norm of everyday conduct concerning the appeal to busyness. Such "practical pedagogy" is an atypical profile for an Academic Platonist, whose standard occupations are dialectic, theoretical ethics, physics; but quite characteristic of an ethically-inclined Platonist of the second century, of whom there were many among the Middle Platonists of the period (cf. Albinus, Apuleius-philosopher, Atticus).

• 01-12 — the only direct mention of Alexander the Platonist by name and by epithet in the Meditations; the source of the single biographical detail we have (plus the school-attribution).
• 01-17 — the thanksgiving to the gods for "having received good teachers"; Alexander is implicitly among them.

• Philostratus, Vitae Sophistarum — the principal prosopographical source for Alexander Peloplaton (book two, in a developed portrait). Standard text: Kayser, Teubner (19th c., reprints); English translation — Wright (Loeb, 1921). NB: the question of the identification of Peloplaton with Marcus's "Alexander the Platonist" is a separate matter, not settled by Philostratus.
• SHA Marcus — the section on Marcus's education (chs. 2–3); Alexander the Platonist is not explicitly named in the SHA as it has come down to us.
• Brunt, P. A., "Marcus Aurelius in His Meditations," JRS 64 (1974) — the classic article on the sources and addressees of Book I; includes a sceptical re-examination of the identifications in Book I, Alexander among them.
• A. Birley, Marcus Aurelius: A Biography, rev. ed., Routledge, 2000, ch. 3 ("Education") — the biographical reconstruction of Marcus's tutorial environment with a cautious attitude toward the identification of Alexander.
• A. S. L. Farquharson, The Meditations of the Emperor Marcus Antoninus, Oxford 1944, vol. II, ad 1.12 — the standard philological commentary, with discussion of the identification.
• R. Hard, Marcus Aurelius: Meditations, OWC, Oxford 2011, notes ad 1.12.
• P. Hadot, The Inner Citadel, tr. M. Chase, Harvard 1998 — the section on Marcus's teachers in Book I (consult the index s.v. "Alexander the Platonist").
• G. R. Bowersock, Greek Sophists in the Roman Empire, Oxford 1969 — contextual reconstruction of the Second Sophistic, in which Alexander Peloplaton occupies a noticeable place.
• PIR² A 503 (for Alexander Peloplaton; the exact prosopographical entry number should be verified against PIR² edition).