Well, it's a bit tricky to say exactly who invented the month names and calendars, as they were created by different cultures at different times in history. But we can tell you that the earliest known calendars date back to ancient civilizations like the Sumerians, Babylonians, Egyptians, and Greeks.

The Romans, who ruled a large part of Europe during the time of Julius Caesar, were among the first to create a calendar system that we're still using today. They divided the year into 12 months, with each month named after a Roman god or goddess. For example, January was named after the Roman god Janus, who was often depicted with two faces - one looking forward and the other looking back.

So, while we can't say for sure who invented the calendar, it's clear that many different cultures have contributed to the development of the calendar system that we use today.