What is Legion about?

Legion, also known as the Gadarene demon, or translated as Lots, is a demon found in the Christian Bible in Mark 5:9 and Luke 8:30. A parallel version of the story can be found in Matthew 8:28-34, but this version does not contain the name "Legion" and tells of two men, not just one, possessed by a multitude of demons. In the story, Jesus traveled to "the country of the Gadarenes" (Luke 8:37), "the country of the Gergesenes" (Matthew 8:28), or "the region of the Gerasenes" (Mark 5:1) and met a man possessed by an evil spirit, which spoke to Jesus in a conversation. The most commonly quoted version is found in Mark 5:9:

And he asked him, What is thy name? And he answered, saying, My name is Legion: for we are many. [it is argued that the phrasing is, "we are legion, for we are many"

A Legion is from 5,000 to 10,000. Yes that is "many".