Daniel Solace is not a real person. He is a program originally created by Maura (or Ciaran).
His name gives it away. Daniel as in the biblical figure who is a wise interpreter of dreams and visions; and Solace, because he was created to comfort and console Maura. This is why he has apparent free range of the various layers of simulation, and is the only one (apart from equally mysterious Elliot) who is aware of the situation. He is also the only main character not to be seen in the room when Maura wakes up on the spaceship.
