ISTJ. Quiet, serious, earn success by being thorough and dependable. Practical, matter-of-fact, realistic, and responsible, often seen as they the big bosses of all the MBTI types. They are extraverted, which makes them charismatic, outgoing and inspirational leaders. are at the top of this list because what they tend to focus on is usually what constitutes intelligence and what is measured by traditional IQ tests: abstract conceptual logic and problem solving.