In Stranger Things, no one is confirmed to have created the Upside Down; it is presented as a pre‑existing parallel dimension whose true origin remains unknown in the show.

Eleven and the Upside Down

• Eleven did not create the Upside Down; she opened a gateway to it during experiments at Hawkins Lab, which allowed contact between our world and that dimension.

• Her powers also banished Henry Creel (Vecna) into that dimension, but that event is shown as her sending him somewhere that already existed, not inventing it.

What the show explains

• The Upside Down is depicted as a dark mirror of Hawkins, discovered accidentally when scientists were experimenting with Eleven’s abilities and tore a hole between worlds.

• The creatures there, led by the Mind Flayer, appear to rule or dominate that realm, but the series has not revealed who or what originally made the Upside Down itself.

Creator statements and theories

• Millie Bobby Brown has stated, citing the Duffer Brothers, that Eleven only opened a portal and did not create the Upside Down, addressing a common fan theory that she made it with her powers.

• Fan discussions propose many possibilities (such as the Mind Flayer or cosmic forces), but none of these theories have been confirmed canonically by the show’s creators.