The Clown
The Clown was the holographic manifestation of the fears of five individuals who were part of a linked neural network.  

The network had been set up by members of Viorsa's species to keep their minds active while they waited in stasis for fifteen years until they could be rescued. Their planet had suffered an environmental catastrophe. Unfortunately, they had not foreseen that the feedback between their minds and the network would create a nexus for their darkest fears; essentially, they were so afraid that something would go wrong that The Clown, a malevolent manifestation of their worst fears, was created from their own fear of death, turning their dream state into a violent and torturous environment.

The Clown demonstrated mood swings and erratic behavior. For nineteen years he tortured the inhabitants of the network, killing three of them by subjecting them to the 'illusion' that they were being placed in a guillotine, but at the same time refusing to let them leave as that would end his own existence. The environment was that of a circus, with different characters such as a Little Woman and The Spectre.

In 2372, the crew of the  found the Kohl settlement after receiving an automated signal. Harry Kim and B'Elanna Torres entered into the dream state of the surviving aliens in order to help them. The Clown threatened to cut off Kim's head, but didn't when Viorsa told him that if he did, Kim's shipmates would turn off the program. Having permitted Torres to leave to explain the situation to the rest of the crew, The Clown subsequently turned Kim into first an old man and then a baby, nearly forcing Kim to relive a memory where he witnessed people having to undergo extensive surgery after an accident. Although Captain Janeway attempted to negotiate with The Clown by sending The Doctor into the environment – as The Doctor was a hologram himself, The Clown was unable to tap into his psyche – their attempts to negotiate were unsuccessful, resulting in The Clown killing Viorsa when he found him helping the crew as they attempted to shut down the program. The Clown was tricked into releasing the other aliens and Harry Kim in exchange for Janeway. While they connected her mind to the system, they were able to configure it so that she remained conscious, her mind linked to the system without actually becoming part of it, while a hologram was used to fool The Clown into believing she was really there until the hostages departed. As the system shut down around him, The Clown admitted his own fear before disappearing into darkness.  His last word was "drat".  ()

de:Der Clown
fr:Le Clown
it:Il Clown
Holograms