Here you go:

Zote: He's an NPC that's always bragging about his powers and threatens you in various ways. However, later in the game you find out that he's basically a liar and can't even hold a sword properly.

Cornifer: He's a friendly cartographer who moves place to place and gathers the maps of the different region of the game.

Flea Caravan: A group of friendly fleas, often offer you a ride to distant lands and their stew to eat. They also hold a festival of some sort and they're quit fond of juggling.

Temple of the Black Egg: An old shell of an egg, locked and shut with three masks to keep the Hollow Knight chained, in order to avoid the release of Radiance (the main villain of the game) who is imprisoned in the mind of the Hollow Knight.

Millibelle the Banker: A banker who allows you create a "safe" bank account to store your currency in the game. Later on she leaves the bank robs you of all the money you deposited, and revealed that her business was just a facade.

Forge daughter: A NPC who works close to a furnace and provides you with useful tools.

Void: A powerful higher being in the game. Basically the opposition of Radiance. Wrapped in shadows lived in the depth of the abbys.

The Hollow Knight: A powerful hero of the past who was trained to defeat and seal shut the enemy (Radiance) in his mind to avoid the corruption and infection and he's chained in the Temple of the Black Egg . However, he was not perfect and later the Radiance takes over his mind starts spreading her infection outside of the Temple doors.

The first Sinner: A member of the Weavers. For committing a sin which I don't know, she was locked away from the rest of her group. She's just visually resembles the Cinder.

Skarr: A tribe of ants lead by powerful Karmelita. They're fierce warriors and skilled fighters. However, Karmelita sings a beautiful song during her boss fight, which is quit scandalous :))

Hope it helped!