Sol Invictus / Mithras, surrounded by the signs of the zodiac
Lion-headed human form, entwined by the serpent (leontocephaline)
The name of the figure has been deciphered from dedicatory inscriptions to be Arimanius (though the archeological evidence is not very strong), which is nominally the equivalent of Ahriman, a demon figure in the Zoroastrian pantheon. Arimanius is known from inscriptions to have been a god in the Mithraic cult.
While some scholars identify the lion-man as Aion (Zurvan, or Kronos) others assert that it is Ahriman. There is also speculation that the figure is the Gnostic demiurge, (Ariel) Ialdabaoth. Although the exact identity of the lion-headed figure is debated by scholars, it is largely agreed that the god is associated with time and seasonal change.