Boogeyman

The boogeyman was a monstrous character in Earth culture, the bogeyman did not have a given appearance or characteristics, but was the embodiment of. fear

In 2370, as Jean-Luc Picard finished a conversation with Mr Boothby, the Starfleet Academy groundskeeper, the gardener warned Picard not to let the boogeyman get him. Moments later Picard was attacked by a Tellarite assassin.