A "sacerdos" or priest with a single Greek name is included in the inscription. He may well be a slave.1
CIMRM entry
312. White marble statue (H. 1.60 Br. base 0.52), found in the Mithraeum on the right
side. Beside the entrance of the Biblioteca Vaticana.
Labus, Bibl. Ital. V (May 1816), 208f; Zoega, Abh., 198, 1 and Pl. XV, 16;
Lajard, Rech., 584 and Intr. Pl. LXX; Millin, Gal. Myth., XVIII, 4 (who
mistakes it for a monument from Rome, No. 545); Clarac, Mus. Sculpt., No.
1193, Pl. 559; O. Müller, Denkm., II (4), 7lf and Pl. 75, 967; MMM II 238f
No. 80 with fig. 68; Roscher, Myth. Lex., 3039 and fig. 1; RRS I, 296, 3;
Eisler, Weltenmantel II 412 f and fig. 50; Paschetto in Bilychnis 1912, fig. 2=
Ostia, 170 fig. 34; Autran, Mithra, 128 fig.; Gressmann, Gestirnrel., fig. 3;
Cecchelli in Roma 1941, PI. XIX; D. Levi in Hesperia XII, 1944,275 fig. 4;
Becatti, 119 and Pl. XXXVI, 1; Alinari 35666 (see fig. 85).
Standing, naked figure with lion's head and wide open. mouth. Behind his
shoulders he has two small wings and two more on his hips. These wings have been
placed in opposite directions and carry the symbols of the four seasons. They are
decorated with a dove and a swan (top right), ears (top left), a bunch of grapes
(bottom left), two palms and a reed (bottom right). The god is entwined in six
coils of a serpent, which rests its head on the god's (Aion). On his breast a thunderbolt.
In his hands which he presses against his body, he holds a key with twelve
drill-holes, and in his left moreover a long staff or sceptre with a knob on either
side. On the base beside the r. leg of the god a pair of tongs and a hammer (Vulcanus)
and beside the l. leg a caduceus, a cock and a pine-cone. Above it the inscription
No. 313. The whole statue was painted red.
313. CIL XIV, 65; MMM II No. 137.
C. Valeri/us Heracles pat(er)
/et C(aii) Valerii
/Vitalis et Nico/mes sacerdo/tes s(ua) p(e)c(unia) p(o)s(ue)r(unt).
/ D(e)d(icatum) idi(bus) aug(ustis) im(peratore)/ Com(modo) / VI et /Septi/miano / co(n)s(ulibus).
190 A.D. In spite of the condemnatio memoriae of Commodus, his name was not obliterated
here, which is due to the fact, that this Emperor himself had been initiated in the
mysteries (Cumont).
John Hugo Wolfgang Gideon Liebeschuetz, "The expansion of Mithraism among the religious cults of the second century", In: "Decline And Change in Late Antiquity: Religion, Barbarians And Their Historiography", Ashgate, 2006, p.195-216. P.201 and p.200: "It is a mark of Mithraism when it first becomes visible that its adherents were socially fairly humble."