Question: Which Greek Stoic philosopher mentioned two of the four subgroups of the Helvetians that failed in their migration attempt to Gaul?
Context: Persaeus (Greek: Περσαῖος ; 307/6–243 BC ) of Citium, son of Demetrius, was a Greek Stoic philosopher, and a friend and favourite student of Zeno of Citium. Aristo of Chios (Greek: Ἀρίστων ὁ Χῖος "Ariston ho Chios"; fl.  c. 260 BC) was a Stoic philosopher and colleague of Zeno of Citium.  He outlined a system of Stoic philosophy that was, in many ways, closer to earlier Cynic philosophy.  He rejected the logical and physical sides of philosophy endorsed by Zeno and emphasized ethics.  Although agreeing with Zeno that Virtue was the supreme good, he rejected the idea that morally indifferent things such as health and wealth could be ranked according to whether they are naturally preferred.  An important philosopher in his day, his views were eventually marginalized by Zeno's successors. Archedemus of Tarsus (Greek: Άρχέδημος ὁ Ταρσεύς ) was a Stoic philosopher who flourished c. 140 BC.  Two of his works: "On the Voice" (Greek: Περὶ Φωνῆς ) and "On Elements" (Greek: Περὶ Στοιχείων ), are mentioned by Diogenes Laërtius. Cleanthes ( ; Greek: Κλεάνθης "Kleanthēs"; c. 330 BC – c. 230 BC), of Assos, was a Greek Stoic philosopher and successor to Zeno of Citium as the second head ("scholarch") of the Stoic school in Athens.  Originally a boxer, he came to Athens where he took up philosophy, listening to Zeno's lectures.  He supported himself by working as a water-carrier at night.  After the death of Zeno, c. 262 BC, he became the head of the school, a post he held for the next 32 years.  Cleanthes successfully preserved and developed Zeno's doctrines.  He originated new ideas in Stoic physics, and developed Stoicism in accordance with the principles of materialism and pantheism.  Among the fragments of Cleanthes' writings which have come down to us, the largest is a "Hymn to Zeus".  His pupil was Chrysippus who became one of the most important Stoic thinkers. Chrysippus of Soli ( ; Greek: Χρύσιππος ὁ Σολεύς , "Chrysippos ho Soleus" ; ) was a Greek Stoic philosopher.  He was a native of Soli, Cilicia, but moved to Athens as a young man, where he became a pupil of Cleanthes in the Stoic school.  When Cleanthes died, around 230 BC, Chrysippus became the third head of the school.  A prolific writer, Chrysippus expanded the fundamental doctrines of Zeno of Citium, the founder of the school, which earned him the title of Second Founder of Stoicism. Posidonius (Greek: Ποσειδώνιος, "Poseidonios", meaning "of Poseidon") "of Apameia" (ὁ Ἀπαμεύς) or "of Rhodes" (ὁ Ῥόδιος) (c. 135 BCE – c. 51 BCE), was a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher native to Apamea, Syria. Epictetus ( ; Greek: Ἐπίκτητος , "Epíktētos"; AD 55 135) was a Greek Stoic philosopher.  He was born a slave at Hierapolis, Phrygia (present day Pamukkale, Turkey) and lived in Rome until his banishment, when he went to Nicopolis in northwestern Greece for the rest of his life.  His teachings were written down and published by his pupil Arrian in his "Discourses" and "Enchiridion". The Helvetii (Latin: "Helvētiī" ] ) were a Gallic tribe or tribal confederation occupying most of the Swiss plateau at the time of their contact with the Roman Republic in the 1st century BC.  According to Julius Caesar, the Helvetians were divided into four subgroups or "pagi."  Of these Caesar only names the Verbigeni and the Tigurini, while Posidonius mentions the Tigurini and the Tougeni (Τωυγενοί ).  They feature prominently in the "Commentaries on the Gallic War," with their failed migration attempt to southwestern Gaul (58 BC) serving as a catalyst for Caesar's conquest of Gaul. Panaetius ( ; Greek: Παναίτιος ; c. 185 - c. 110/109 BC ) of Rhodes was a Stoic philosopher.  He was a pupil of Diogenes of Babylon and Antipater of Tarsus in Athens, before moving to Rome where he did much to introduce Stoic doctrines to the city.  After the death of Scipio in 129 BC, he returned to the Stoic school in Athens, and was its last undisputed scholarch.  With Panaetius, Stoicism became much more eclectic.  His most famous work was his "On Duties", the principal source used by Cicero in his own work of the same name. Sandon (Greek: Σάνδων ; 1st century BC) is an Orphic philosopher mentioned in the "Suda".  He is described briefly as a son of Hellanikos.  He has been identified with the Sandon of Tarsus mentioned by Pseudo-Lucian in the essay "Macrobii" ("Long Lives"), who was the father of Athenodorus (the Stoic philosopher and the tutor of Augustus Caesar).  His father Hellanicus may have been the Orphic philosopher of the late 2nd century mentioned by Damascius.
Answer: Posidonius