The term "Dark Triad" was coined in 2002 by psychology researchers Delroy L. Paulhus, Ph.D., and Kevin M. Williams, Ph.D., from the University of British Columbia. But scientists have been studying each of these traits individually for decades: Psychological research on narcissism dates back to Austrian psychoanalyst Otto Rank's 1911 paper on the topic, and published research on Machiavellianism dates back to the 1970s with professors Richard Christie and Florence Geis.
The triad and its traits have been popular areas of psychological study for the entire two decades since the phrase was initially used. Paulhus now leads a psychology research lab, and his work has been cited over 43,000 times in scholarly journals and books, many of which are specifically about these dark traits.
Some researchers had previously characterized the triad's behavioral manifestations as just variations of one singular personality type, although Paulhus and Williams' 2002 study found them to be distinct. Jonason also points out that some researchers actually believe that the Dark Triad is simply a manifestation of the Big Five personality traits, i.e., openness to experience, conscientiousness, extroversion, agreeableness, and neuroticism.
Zeigler-Hill notes many contemporary studies are trying to pinpoint how the Dark Triad functions in romantic relationships. He says, "I think the clearest of these studies address the multidimensional nature of these traits instead of treating them as if they are unidimensional."
For example, a recently published study by researchers in Slovakia tackled the relationship between the Dark Triad and romantic relationships among young adults. Zeigler-Hill says studies like this show the importance of distinguishing between assertive/extroverted narcissism, antagonistic/disagreeable narcissism, and vulnerable/neurotic narcissism, which each diverge in in their associations with romantic outcomes. (Here's more on the various types of narcissism.)