1. Noun, Pronoun: A derogatory term used to desribe a bearer of bad news.

2. Noun: A messenger bringing unwated or undesirable information.

Similar in usage to 'Gloomy Gus'
Often misspelled with a 'c' replacing the 'k', however the 'Mark' is meant in a literal nature (as in mark your calendar), as opposed to 'Marc', which is defined as a personal noun.