For this man see already pi 1326 and especially sigma 63 (latter part), where he is presented as 'a commander of the palace under [the emperor] Julian'. Banchich (1988: 224) suggests that he must be Julian's praetorian prefect Saturninius Secundus Salutius (sic), mentioned by Eunapius of Sardis in this Suda passage (= Eunapius, Fragmenta Historica 1.231.13-25 Dindorf) -– and in his extant Life of the Sophists 479 (52.20, 53.9-10, ed. Giangrande). When Julian died, the army offered the succession to Salustius (Fowden 1997: 547). Salustius (or Salutius -- see Banchich 1988: 224, n.6) was Julian’s close friend and adviser; he wrote a treatise On the gods and the world, where he defended, inter alia, the thesis of the ingenerability, eternity (2.1), and incorporeality (2.2) of god. He also argued for the immortality of the soul (8.3).
If the 'Sallustius' of these Suda passages (and elsewhere) is not Saturninus Secundus Salutius, an alternative theory identifies him with the Flavius Sallustius was was praetorian prefect of Gaul 361-363.
[1] Valentinian I (omicron 762); he served under Julian, amongst others, before becoming emperor himself.
[2] This unusual use of the verb diade/xomai is noted in LSJ s.v.
[3] That is 'a person placed over', a common title given to many officers in the later Roman Empire. In the Suda cf. under epsilon 3604 (= theta 145 = pi 793 = upsilon 169).
[4] 'Chrysaphius' in pi 2441, q.v.