I'm a Christian and I don't believe in a single being who rule over demons such as "satan". Demons are unclean spirits that came out of the nephilim when they died in the flood. Satan is not a name, it means accuser and anybody can be called satan such as Peter. There is no one being called satan, the term can apply to anyone based on there actions. As for the angels who came to earth that fooled Eve and had realtions with women, they are not roaming the earth but are being held in Tartarus until there destruction.
2 Peter 2: 4 For if God did not spare angels when they sinned, but sent them to tartarus, putting them into gloomy dungeons to be held for judgment;