The King of Hallownest was faced with ridding the world of the Radiance, which was causing the Infection. The Infection turned bugs into zombie-like creatures, like we see throughout the game. To do this, the King created vessels from his (and the Queen's) children. These vessels were meant to be emotionless and raised to house the Radiance in their minds, to lock it away. The vessels were born in the Abyss and filled with Void. They were meant to be "hollow" shells with just the void inside of them. The Hollow Knight was the Vessel chosen to be raised to house the Radiance, and the Knight (the main character) is its sibling but was not chosen.
The Hollow Knight was not hollow enough to seal away the Radiance effectively though. Being raised by the Pale King gave it too much humanity (for lack of a better word) and it wasn't fully emotionless. When it was sealed away in the Black Egg temple with the Radiance in its mind, as was planned, the Radiance seeped out and caused the Infection to grow again.
The Dreamers sealed the Hollow Knight in the Temple, but it was expected to be to keep the Radiance locked away for all eternity. They weren't expecting it to seep out and infect everything.
The Knight somehow escaped from the Abyss and left Hallownest for an indeterminate amount of time. When it returned, it had to hunt down and kill the Dreamers (which they welcomed) to open the Black Egg temple, which allowed it to face and destroy the Radiance and stop the Infection.
Hornet is the King's daughter, with the Weaver rather than the Queen, which is why she's more powerful than most bugs and knows so much about Hallownest and the royalty.
The King of Hallownest was faced with ridding the world of the Radiance, which was causing the Infection. The Infection turned bugs into zombie-like creatures, like we see throughout the game. To do this, the King created vessels from his (and the Queen's) children. These vessels were meant to be emotionless and raised to house the Radiance in their minds, to lock it away. The vessels were born in the Abyss and filled with Void. They were meant to be "hollow" shells with just the void inside of them. The Hollow Knight was the Vessel chosen to be raised to house the Radiance, and the Knight (the main character) is its sibling but was not chosen.
The Hollow Knight was not hollow enough to seal away the Radiance effectively though. Being raised by the Pale King gave it too much humanity (for lack of a better word) and it wasn't fully emotionless. When it was sealed away in the Black Egg temple with the Radiance in its mind, as was planned, the Radiance seeped out and caused the Infection to grow again.
The Dreamers sealed the Hollow Knight in the Temple, but it was expected to be to keep the Radiance locked away for all eternity. They weren't expecting it to seep out and infect everything.
The Knight somehow escaped from the Abyss and left Hallownest for an indeterminate amount of time. When it returned, it had to hunt down and kill the Dreamers (which they welcomed) to open the Black Egg temple, which allowed it to face and destroy the Radiance and stop the Infection.
Hornet is the King's daughter, with the Weaver rather than the Queen, which is why she's more powerful than most bugs and knows so much about Hallownest and the royalty.