January is named after Janus, the Roman god associated with beginnings, transitions, doorways, and change.
Janus is traditionally depicted with two faces, one looking forward and one looking backward. That imagery made the god an apt namesake for the first month of the Roman and later Gregorian calendar year: January looks back at the year that ended and forward toward the year beginning.
The Latin name for January is Ianuarius. The month was associated with Janus in Roman religious tradition, and the English word “January” developed through later forms of that name.
Janus should not be confused with Saturn, another Roman god strongly connected with winter celebrations through the festival of Saturnalia. Nor is Janus the god who gave his name to the weekday Saturday. The connection between Janus and New Year is symbolic and calendrical rather than a claim that he personally founded modern New Year’s Eve customs.