The Minds in Iain Banks' book Excession create meta-realities in their imaginations, and allow entire universes to run through from beginning to end.

They can also create autonomonous beings, and therefore could presumably allow these beings to exist inside the mets-realities that they create.

To the beings inside these universes, they would believe whatever the Mind wanted them to believe, although it probably would allow the beings to choose their own path.