Quirrel

Quirrel is an inquisitive, up-beat explorer, fascinated by the myths of Hallownest for reasons he can not explain. While he remains a simple observer, he is wise of the land's dangers and has some skill with a nail.

Lore
Before the fall of Hallownest, he used to be Monomon’s apprentice. When Monomon became a Dreamer, she entrusted Quirrel with her mask, which was part of an additional protection enacted upon herself. Quirrel can be seen wearing this mask on top of his head.

In the official comic, it is shown that Quirrel ended up outside of Hallownest, causing him to lose much of his memory. He was called back to Hallownest by Monomon in order to reverse the protection placed on her. After entering the Howling Cliffs, Quirrel meets Hornet, whom he briefly fights. Hornet allows Quirrel to enter Hallownest when she recognizes Monomon’s mask.

Quirrel can initially be found at the Temple of the Black Egg, but he can be encountered in several locations around Hallownest. After helping the Knight kill Monomon by removing the protection on her, he goes to Blue Lake to see the source of the rain in the City of Tears.

First Encounter, Temple of the Black Egg
Quirrel is first met staring at the Black Egg in wonder. He briefly talks about how he feels drawn to the egg. He also explains that many travellers have come down into the ruins and fallen, and lightly suggests that they may have useful belongings that the Knight could use. Once the player has defeated False Knight, Quirrel will no longer be present at this location.

Second Encounter, Lake of Unn
Quirrel is found sitting on a rock next to the bench inside the structure, polishing his nail. He tells the Knight that its blade is looking a little worn, and that it may not fare as well below the surface.

Third Encounter, Queen's Station
Inside the station, Quirrel can be found sitting on the edge of a platform above the entrance to the Stagway.

Fourth Encounter, Mantis Village
If the Knight still wields the Old Nail and has entered the south part of Mantis Village where the Mantis Lords can be found, Quirrel can be encountered in the east part of Mantis Village where he hints at seeking out the Nailsmith before proceeding further past the boss fight.

Fifth Encounter, City of Tears
Quirrel is found sitting on a bench on the way into the City of Tears, looking out the window. He tells the player he feels pulled into the city, but is hesitant to enter, not knowing why. He mentions the water coming down endlessly from above and that he wants to see where it comes from before he leaves the Kingdom.

Sixth Encounter, Deepnest
He is next found resting in the Hot Spring in Deepnest after the Failed Tramway has been visited. He hints at the existence of a village in Deepnest, home to those who never accepted Hallownest's King.

Seventh Encounter, Crystal Peak
Quirrel is found standing next to a huge window at the peak, looking down onto Dirtmouth, pondering.

Eighth Encounter, Outside the Teacher's Archives
Found just outside the entrance to the Teacher's Archives, somewhat confused, feeling drawn inside. He later appears during the Uumuu boss fight to help the Knight by puncturing the outer membrane of the boss, allowing the Knight to damage them.

Ninth Encounter, before Monomon
After inspecting the tank that Monomon the Teacher is inside, Quirrel will jump up from below. He explains the history of the Teacher and that he played a part in her protection. He holds up his hat, which is revealed to be Monomon's mask, and undoes that protection to help the Knight. Afterwards he sits there until the Knight leaves.

Final Encounter, Blue Lake
In the final encounter with Quirrel, he's found sitting next to Blue Lake, as he said he would want to see where the rainwater is coming from in the City of Tears. He tells the Knight that now, after seeing the world twice over, he finally feels at peace, and he is thankful he could see its beauty again.

After the conversation, the Knight can choose to sit next to him in silence. Doing so rewards the "Witness" achievement.

After leaving the room, Quirrel will have disappeared. His nail can be seen planted into the ground beside the Lake.

Locations
Quirrel can be found in several locations across Hallownest. However, he will not appear in all after he is encountered in Fog Canyon.

Trivia

 * Quirrel is one of four characters in the game that can help during a boss fight. The others are Cloth during the Traitor Lord fight, Hornet while fighting the Hollow Knight, and the Hollow Knight at the end of the Radiance fight.
 * Quirrel takes off Monomon's mask in the Teacher's Archives (after Uumuu is defeated) and in Blue Lake.