Quote Originally Posted by Expat
I disagree, he's more like an ESTj.
No way!

He works tirelessly, day and night, on highly obscure problems in very esoteric specialties, hoping to make some contribution, no matter how small.
he is extraordinarily demanding, and he has a tendency to expect people to make intuitive leaps so as to follow what he’s saying. However, through practice, he has learned to explain things more methodically for people to understand. When explaining something, he has a certain sense of excitement, as if he’s letting you in on some secret, something that only very smart people are allowed to know.

The only thing that points towards ESTj is that he reads the entire book before doing anything.