The Void is the substance of The Abyss. It plays a major role throughout the history of the Kingdom of Hallownest. Most of the Void is found in a sea and smaller pools at the bottom of the Abyss, but multiple beings exist who consist of Void themselves. An ancient civilisation which predates the Kingdom of Hallownest worshipped the Void. This is likely the same civilisation responsible for creating the Soul Totems and Arcane Eggs.
The Void is "the power opposed"; it has the ability to oppose light-based higher beings such as the Radiance and the Pale King, who are both described as a light. The Void is also the Radiance's ancient enemy.
On the east side of the Abyss, a lighthouse was constructed and its light used to suppress the Void Tendrils present in the sea of Void. The sea of Void called to a Royal Retainer corpse in one of these lighthouses. Its eyes appear to be leaking Void, something which it has in common with other Royal Retainer corpses throughout Ancient Basin and the bug corpse which holds the Love Key in Queen's Gardens. In the Embrace the Void ending, The Godseeker's eyes are similarly shown leaking Void before tendrils of Void burst from their body.
The Pale King used the Void to create two kinds of constructs in his workshop in the White Palace, the Kingsmoulds and Wingmoulds. They have a white shell or armour with Void inside them. The Kingsmoulds were used to guard the White Palace, but the purpose of the Wingmoulds is unclear. The Collector takes on a similar appearance to a Kingsmould, although it is not known if they are related.
Also created by the Pale King were numerous Vessels, beings who have a Shade made of Void within their shell. They were created in an attempt to permanently seal away the Radiance once she re-surged and caused the Infection. However, almost all of the Vessels were deemed to be unsuitable to seal her.
Eventually, one Vessel—The Hollow Knight—was judged to be a pure Vessel and chosen to seal the Radiance. After this, the entrance to the Abyss was sealed, only to be opened by somebody bearing the King's Brand.
When The Knight acquires the Void Heart, the Void is unified under their will. In the Dream No More and Embrace the Void endings, The Knight transforms into the Void Entity, and the Void, unified under their will, is used to defeat the Radiance.
- The Collector - Powerful Void being that resides in the Tower of Love. Responsible for the capture of the captive grubs.
- The Hollow Knight - The Vessel deemed "pure" by The Pale King, they were trained and then used to contain The Radiance.
- Kingsmoulds - Constructed with the Wingmoulds in the King's workshop as guards.
- The Knight - The Vessel the player controls throughout the game.
- Pure Vessel - Name given to The Hollow Knight while they were at their prime. Although the name labels The Hollow Knight as "pure," this was only a title given to them as they were believed to be a pure Vessel. The White Lady indicates that their purity was misjudged, as they were tainted by an "idea instilled."
- Shade - The Void within the Knight.
- Siblings - The Shades of the Vessels that were deemed to be not pure enough to seal away the Radiance.
- Void given Focus - Also known as "Shade Lord" in the game files, a colossal being of pure Void that the Knight transforms into upon completing the Pantheon of Hallownest. Referred to as "God of Gods" by The Godseeker.
- Void given Form - The Knight transforms into this being upon defeating Radiance in the Temple of the Black Egg. It resembles The Knight's Shade but with longer tendrils emanating from it.
- Void Tendrils - Possibly a natural formation of the Void itself, as there is no mould for it but rather only an imprint found engraved into a rock in the Abyss.
- Wingmoulds - Constructed with the Kingsmoulds in the King's workshop. Unknown how the shape was created, although several pieces of their armour are found hanging from the ceiling.