Cattell was the founder of the "factor analysis" method of assessing personality. The idea behind factor analysis was that if there was an important facet of human personality to note, it would have already been defined into a single word by people throughout history. So Cattell and his team set to combing the dictionary, "analyzing" each word into a common "factor", until eventually sixteen distinct factors were defined. A person was measured by a scale of preference for these factors. Later, other researchers simplified these factors into smaller parts, leaving only three and then upped to five. These five words are what constitutes the "Big Five" so popular to psychologists today.
Anyway, I have reason to believe that Cattell may have been an INTp. For one, he was lost in his own mind. He would lay in bed for hours thinking about new ideas and running experiments in his mind. He had so many thoughts going through his head, that he often recorded his ideas with a tape recorder (I should get one of those.) He also had a habit of overworking himself, where he would stay in his laboratory until midnight, when everyone was long gone by then. He was incredibly absent-minded, and the only reason he could find his car after work was because it was the only one left in the lot. Beyondism, a religion he invented, seems to me to come from the carelessness of the INTp's common over-confidence.
Just a thought.