Philipp Budeikin is being held in a Russian jail on charges of inciting more than a dozen girls to take their own lives.
Police are alleging Budeikin was the mastermind behind a social media game called the Blue Whale challenge.
It's believed the game was named after blue whales because of the belief that they wash up on beaches to die.
It's a sick, twisted, psychologically manipulating game where people willingly sign up and complete a variety of strange tasks (waking up in the middle of the night, watching a scary movie) and self-harm every day.
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The tactic was to slowly warp participants' minds over 50 days, where the final challenge was to commit suicide.
If that wasn't messed up enough, Budeikin's motive behind it is even more sinister. He's told a news organisation in St Petersburg: "They were dying happy. I was giving them what they didn't have in real life: warmth, understanding, connections.
"There are people - and there is biological waste. Those who do not represent any value for society. Who cause or will cause only harm to society. I was cleaning our society of such people."
Budeikin has admitted to offering encouragement to his victims if they express doubt during the 'game'. He once told one teenage girl that life never gets better, that she wasn't interesting and her parents didn't understand or need her.
He's even told prosecutors he was responsible for pushing a participant to leap to her death from a 14-storey building.
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One of the girls involved in the challenge has opened up about how it warps your mind, telling the Daily Mail: "I had to watch videos with pictures flicking every two seconds of teenagers jumping off roofs, close-ups of bodies, bloodied mouths, pools of blood under bodies. It was accompanied by very unpleasant, haunting music with screams of animals and pets, and cries like children were being tortured.
"I felt so awful after watching them I wanted to do something physical to either myself or somebody, to kill, to destroy."
She told the administrator that she wanted out but he refused to let her, and kept goading her into finishing. But the girl went to the authorities with the messages and told her story.
News of the challenge has prompted police in the UK to send out a warning to children and young adults. The challenge has spread across Europe where cases have been opened in Belgium and France.
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