The Chair is an enormous chair in The Room.
The Chair has many tiny creatures living inside of it. Those creatures eat The Chair for food, just like how the Shadow eats The Table.
The Chair is infinitely big, and stretches infinitely in every direction.
The Chair is usually depicted as an IKEA chair, as shown in the image. However, The Chair is not made from wood, and is instead composed entirely of Primordium Delta.
A groove on The Chair's surface seems to suggest that an entity has sat on The Chair. It is unknown who this entity is, but whoever did that must be extremely huge.
The Chair is burning hot. If you touch The Chair, you will most likely vaporize immediately and die. It is unknown why that happens. The creatures inside The Chair can withstand the scorching temperatures though.