Referring to Keirsey, INTJs belong to the temperament of the rationals and are called Masterminds.
In Socionics INTj belong to the club of the researcher, the alpha Quadra and are named "Analyst", Descartes or Robespierre. Another notation for INTj is LII (which is an acronym for Logical-Intuitive Intratim, referring to the cognitive functions).
INTJs are often found in the sciences or engineering.