Vihaar

From Memory Alpha, the free Star Trek reference.

The Vihaar (also spelled Vahar or Va'har) is a semi-mythical creature within Malon society, especially in waste export worker parlance. The Vihaar was said to be a monster composed of radiogenic wastes and antimatter that roamed the interiors of Malon waste export vessels and wreaked havoc. Until 2375, there was very little evidence for the existence of Vihaars and most Malons considered them to be only a myth, made up by gullible freighter hands or by hallucinating crew members.

In 2375, the myth was proved to have some basis in reality, when it was revealed that a former export vessel core laborer named Dremk, had in fact become theta radiation-resistant and as such, undetectable to most sensors aboard a Malon ship. However, the subsequent resistance also left him physically and mentally damaged and harboring a lot of hatred towards most other Malon. It is believed that this has happened to other core laborers and as a result given the myth some gravity. (VOY: "Juggernaut")