A living example. Marcus Aurelius 1.8
Rusticus may have been the adult Marcus' preferred philosopher, but he has kind words for another one, too. You can hear me read them <here>.
Παρὰ Ἀπολλωνίου τὸ ἐλεύθερον καὶ ἀναμφιβόλως ἀκύβευτον καὶ πρὸς μηδὲν ἄλλο ἀποβλέπειν μηδὲ ἐπ̓ ὀλίγον ἢ πρὸς τὸν λόγον· καὶ τὸ ἀεὶ ὅμοιον, ἐν ἀλγηδόσιν ὀξείαις, ἐν ἀποβολῇ τέκνου, ἐν μακραῖς νόσοις· καὶ τὸ ἐπὶ παραδείγματος ζῶντος ἰδεῖν ἐναργῶς ὅτι δύναται ὁ αὐτὸς σφοδρότατος εἶναι καὶ ἀνειμένος· καὶ τὸ ἐν ταῖς ἐξηγήσεσι μὴ δυσχεραντικόν· καὶ τὸ ἰδεῖν ἄνθρωπον σαφῶς ἐλάχιστον τῶν ἑαυτοῦ καλῶν ἡγούμενον τὴν ἐμπειρίαν καὶ τὴν ἐντρέχειαν τὴν περὶ τὸ παραδιδόναι τὰ θεωρήματα· καὶ τὸ μαθεῖν πῶς δεῖ λαμβάνειν τὰς δοκούσας χάριτας παρὰ φίλων, μήτε ἐξηττώμενον διὰ ταῦτα μήτε ἀναισθήτως παραπέμποντα.
From Apollonius (†) I learned freedom and frank discretion (‡), also to keep my gaze fixed relentlessly upon the argument at hand, without deviating even a little. To remain the same person—whether in great physical pain, in the loss of a child, or in the throes of long illness. From his living example I came to see vividly that an extremely vehement character is capable of relaxing. I learned not to show annoyance when giving explanations. To see that a real man counts his experience and facility in imparting theory as distinctly the least of his virtues. To understand how to take kind gestures from friends without being thereby diminished or refusing to acknowledge them.
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(†) Apollonius of Chalcedon—or the nearby Nicomedia (thus Cassius Dio, 72.35)—was another Stoic philosopher. Wanting a good tutor for his two adopted sons, Lucius Verus and our Marcus, the emperor Antoninus Pius solicited Apollonius away from his home in the East. The Historia Augusta records that the imperial summons to Rome found the philosopher at Chalcis, in Euboea (Antoninus Pius § 10). Lucian of Samosata adds that the Cynic philosopher Demonax witnessed the departure of Apollonius, remarking: “Apollonius and his Argonauts set forth!” (προσέρχεται Ἀπολλώνιος καὶ οἱ Ἀργοναῦται αὐτοῦ: Demonax § 31).
(‡) The Greek adjective ἀκύβευτον literally means not playing dice. The verb κυβεύω (to play dice) that it negates also carries the metaphorical meaning of running voluntary risks.