"Wandering around at midnight, Ickle Firsties? Tut, tut, tut. Naughty, naughty, you'll get caughty."
     -- Peeves

Peeves is a poltergiest and is considered to be one of the Hogwarts ghosts. The other ghosts, however, do not consider him to be a proper ghost (SS7). Peeves is a little man wearing loud, outlandish clothes including a bell-covered hat and an orange bow tie. He is solid-looking, not pearly white and transparent like other ghosts. He has wicked, dark eyes (SS7) Peeves swoops around the corridors and in the classrooms of the castle causing mischief and trouble wherever he can. 

Peeves can become invisible (SS7) and will throw things at people (walking sticks (SS7); water balloons (GF12)). He makes rude noises and tumbles over in the air and peers through his spread legs. His voice is an evil cackle (SS7). Peeves particularly enjoys pestering Filch. The Bloody Baron is the only one who can control Peeves, although he does show some grudging respect for Dumbledore (PA

• Peeves stuck out his tongue and vanished, dropping the walking sticks on Neville's head. They heard him zooming away, rattling coats of armor as he passed. (SS7)

 
• Peeves the Poltergeist was worth two locked doors and a trick staircase if you met him when you were late for class. He would drop wastepaper baskets on your head, pull rugs from under your feet, pelt you with bits of chalk, or sneak up behind you, invisible, grab your nose, and screech, "GOT YOUR CONK!"  (SS8)

 
• Professor McGonagall pointed them into a classroom that was empty except for Peeves, who was busy writing rude words on the blackboard.

"Out, Peeves!" she barked. Peeves threw the chalk into a bin, which clanged loudly, and he swooped out cursing. Professor McGonagall slammed the door behind him and turned to face the two boys. (SS9)
 
• "Which way did they go, Peeves?" Filch was saying. "Quick, tell me."

"Say 'please."'
"Don't mess with me, Peeves, now where did they go?"
"Shan't say nothing if you don't say please," said Peeves in his annoying singsong voice.
"All right--please."
"NOTHING! Ha haaa! Told you I wouldn't say nothing if you didn't say please! Ha ha! Haaaaaa!" And they heard the sound of Peeves whooshing away and Filch cursing in rage (SS