Scarcity of sources. Cinna Catulus is a figure to be reconstructed biographically only minimally. Everything we securely know about him is exhausted by:

1. The mention in Marcus's catalogue of mentors (01-13) — the only developed testimony, and even this reports only the ethical "receipt," not biographical data.
2. Inclusion in the standard list of Marcus's philosophical teachers in SHA Marcus (Vita Marci, ch. 3), where Catulus is named among the Stoic mentors alongside Apollonius of Chalcedon, Junius Rusticus, Sextus of Chaeronea, Claudius Maximus, and others. (The exact segmentation of sub-paragraphs in ch. 3 varies between editions of the SHA; consult Hohl's edition.)

Beyond these two testimonies, no biographical details, no anecdotes, no surviving fragments of writings. The prosopographical handbooks (PIR², prosopographical databases of Roman philosophers) give him a short entry primarily on the basis of these same two sources, without adding reliable information. In Rogovin's footnote to 01-13 he is called "Cinna Catulus," and this form of the name is standard in current academic usage.

School affiliation. Stoic. This is known both from the SHA (where Catulus is directly classified among the Stoic teachers) and indirectly from Med. 1.13 itself: the content of Marcus's thanks (on τέκνα ἀγαπητικόν, on φίλος αἰτιώμενος, on ἐκθύμως εὔφημον περὶ τῶν διδασκάλων) reproduces the general Stoic ethics of σχέσεις and philostorgia, with none of the characteristic Platonic or Peripatetic colourings.

Contrast with the other Stoic mentors. Among the Stoics of Book I, Rusticus (01-07), Apollonius (01-08), and Sextus (01-09) have an external biographical accretion — career data, anecdotes, mentions in Lucian, in Philostratus, in Aulus Gellius, in the SHA Pius. Catulus has no such accretion: no anecdotes about him survive, no mentions in non-philosophical literature of the second century. Marcus mentions him only once, and that entry is the only "portrait" of Catulus available to us. In this respect Catulus is the most "internal" teacher of Book I: he exists for us solely through Marcus's thanksgiving, without external witnesses.

• 01-13 — the only direct and the only developed mention; the source of everything we know about Catulus as a teacher.
• 01-17 — the thanksgiving to the gods for "having received good teachers"; Catulus is implicitly among them.

• SHA Marcus (Vita Marci), ch. 3 — the catalogue of Marcus's philosophical teachers, where Catulus is reckoned among the Stoics. Standard text — Hohl, Teubner; the precise segmentation of sub-paragraphs should be verified against the edition.
• A. Birley, Marcus Aurelius: A Biography, rev. ed., Routledge, 2000, ch. 3 ("Education") — the reconstruction of Marcus's Stoic educational environment; for Catulus, Birley records the same scarcity of sources.
• A. S. L. Farquharson, The Meditations of the Emperor Marcus Antoninus, Oxford 1944, vol. II, ad 1.13 — the standard philological commentary; discusses, among other matters, the unsuccessful attempts to identify Domitius and Athenodotus.
• R. Hard, Marcus Aurelius: Meditations, OWC, Oxford 2011, notes ad 1.13.
• P. Hadot, The Inner Citadel, tr. M. Chase, Harvard 1998 — the general reconstruction of Marcus's Stoic education (consult the index for any entry on Catulus).
• PIR² — a short prosopographical entry mainly on the basis of the SHA and the Meditations (the exact entry-number should be verified against PIR²).