The Spiral is one of several powers called The Entities that influence our world. The Spiral is among the most mysterious, largely due to its nature, which involves distortion, impossible geometry and maddening realms and dimensions.
The most encountered manifestation or avatar of The Spiral is Michael who can open doors in various places that lead to other places, occasionally to another place in our world, usually to an endless labyrinth. Helen Richardson was taken by one such door and Martin and Tim were saved from Not Sasha by Michael through this creation.
The Spiral's motivations are not yet fully known, however it has been shown to create areas of distortion in our world, such as in Sannikov Land where the entire island is defined by impossibility and structures that should not be able to exist.
Its allegiances are similarly difficult to fully know. It seems to want balance or a delay in events as Michael explained in the tunnels when combating Not Sasha. It also helped the real Sasha fight a manifestation of The Hive. It seems to be in a tentative alliance with Beholding (although this seems only to prevent other Entities from gaining power) and actively fights against The Hive, and more frequently against The Stranger.