Do We Have This One?? When one or more characters have the ability to create worlds at will, through magic, technology or anything else. It doesn't matter if said worlds aren't "real" (as seen in the Matrix with the machines) as long as sentient entities (if any) inside at least one of these worlds can be conscious (even if all other worlds created in the same fashion are uninhabited), but the general rule of thumb is that said characters generally create not one, but at least a few different worlds (as seen in Myst, with the D'ni). It's different from some multiverses in that in the story itself there is one or more creators of said worlds (that is, the multiverse wasn't introduced in the story just to host many different authors having different perspectives on the same heroes or events), and some action may take place between these worlds or outside of them (or in one that servers as a hub between them). The creator isn't necessarily evil or a ruler of the worlds he creates.
- Myst: This is the most bold example I have for this trope. The D'ni were habitual world creators. I know that they viewed the Art as linking to worlds, rather than creating them, but since they base this on their "infinite universes" philosophy, this is rather a difference of semantics (in the same way that I could say that I didn't create this chunk of text, but simply found myself in one of the universes in which this exact text is posted).
- The Matrix: The Architect could be considered this, since there were different versions of the Matrix.
Hello, Unknown Troper. You'll need to get known to lend a hand here.