It's the stuff nightmares are made of.

This week, a parent complained to police after two teens dressed as clowns, one of whom was carrying a two-metre-long chain, chased children home from Parc Limbour, in northwest Gatineau.

The subsequent news headlines all used the same word: creepy.

It's not the first case of its kind.

An Italian YouTube channel, DM Pranks, has earned millions of hits for featuring clips of menacing clowns behaving strangely or bludgeoning stuffed dummies in public.

The idea of the terrifying clown was perhaps most famously executed in the Stephen King novel, and subsequent movie, It, where the clown Pennywise preyed on children.

The fear of clowns is so deeply rooted in human psyche it even has its own (albeit unofficial) name: coulrophobia.

But why is the deranged clown a trope we return to in frightening books, movies, and television?

Aalya Ahmad, an adjunct professor at Carleton University who teaches a class on horror, said clowns have a long history of being scary, beginning with their manic medieval beginnings.

Unpredictability factor

"The clown goes back to the tradition of the jester, or the holy fool, and the jester was the only one who had licence to speak freely to the king and nobles," she explained to CBC's All in a Day host Alan Neal.

Ahmad said nobles would count on the jester if they didn't trust their cohorts, but underneath the ridicule was a dose of harsh reality.

Halloween Regina

Frank McAndrew, a Cornelia H. Dudley Professor of Psychology at Knox College, led a first-of-its-kind study on what people find creepy. Topping the list of creepiest professions? Clowns, followed by taxidermists and sex shop owners. (Dean Gutheil/CBC)

"The clown and the monster both kind of get to go on these rampages and expose some of the fears that we hide," she continued. "It's less predictable than a zombie...The joker is wild, we don't know what they're going to do."

Deranged clowns also cruelly twist the childhood association many people have with them. It's innocence gone "horribly wrong," said Ahmad.

They "expose some of the cracks in society through their innocence, through their childlike quality."

Mask of death

Clowns also play on the idea of the uncanny.

"You have this body, an adult human body, but you have this unfamiliar head. You see those pictures from Gatineau Park are extremely creepy," she said.

"What scares us about masks is they're highly artificial...The uncanny plays on that idea of the familiar becoming unfamiliar very suddenly."

Ahmad said other critics have noted that the only other time a person's face is frozen like a painted-on clown's face is in death.

"White faced as a death mask with a sense of humour," she said.

Of course, not all clowns are terrifying.

Toronto's Doo Doo the Clown saved a woman from a vicious attack last November.

Diane Sonnenberg said a man lashed out and began hitting her.

WARNING: Contains strong language. Doo Doo the Clown's dash cam captures moment when attacker jumps on SUV.0:32

It was then that Doo Doo the Clown, best-known for his role in the Adam Sandler film Billy Madison, came out of nowhere to save the day.

"I remember pulling up as fast as I can screaming, 'Get in, get in!' and I know that I am a clown and I had a car full of clowns, but these ladies ran and jumped into the back," said Doo Doo in a phone interview with CBC News.

News of the rescue prompted Coun. Norm Kelly to award Doo Doo with a scroll recognizing his act of bravery.