Janus is unique among In Nomine’s heavenly pantheon in that he was once worshiped as a god in the real world.
Specifically, Janus was a Roman god of beginnings, endings, and transition. He was invoked on doors and gates, at the start of religious rites, the change of seasons and at the onset and conclusion of war. The month of January is named in his honor (though the Romans actually dedicated it to Juno), and he was typically depicted as a being of two faces, one young and one old.
The contemporary image of old man December and newborn January is likely drawn from Janus iconograpy.
Priests and Worship
While Janus did have a cultic following, he rather notably lacked a dedicated priesthood. Among his followers he was known as the Opener, the Gatekeeper, the Good Creator, the Two Faced, the Janitor, the best and most powerful of kings, and the father of gods.
On account of the first two he is sometimes associated with Mercury, on account of the last he is sometimes associated with Jupiter and Uranus.
Ties to In Nomine
Among the many things Janus was associated with, time and movement, and thus change were principle among them. Likewise, his connection to War is reflected in his mythic roots. Associations with Wind and Theft are inventions of the RPGs authors, but they do make for a more dynamic and compelling superior.
Janus Bifrons (or the Two Faced Janus) is his most well known contemporary aspect. You can see it in the New Year’s Race in Sandman. You can see it in the sculptural representations of the god. You can see it in what aspects of the god we still use in everyday life.
With this in mind, the near identical nature of Janus and Valefor is a strong argument in favor of both being the same entity. Croc goes even further in the original In Nomine Sanitas/Magna Veritas – equating Janus directly with Hermes, who has been hiding among the Host of Heaven and the Princes of Hell.