The Nameless One is a villain in the Marvel Universe, and is an enemy towards the Defenders.
The Nameless One is the leader of an ancient race of demons known as the Undying Ones who use to rule the Earth a millennia ago. Eventually, their power waned and they were forced to return to their own dimension. In modern times they were temporally able to reach our dimensions and attempted to invade earth. They would come across the Defenders countless times, and every time, they would be sent back to their dimension.