ISTP

For ISTPs the driving force in their lives is to understand how things and phenomena in the real world work so they can make the best and most effective use of them. They are logical and realistic people, and they are natural troubleshooters. When not actively solving a problem, ISTPs are quiet and analytical observers of their environment, and they naturally look for the underlying sense to any facts they have gathered. ISTPs often pursue variety and even excitement in their hands-on experiences. Although they do have a spontaneous, even playful side, what people often first encounter with them is their detached pragmatism.

......From Looking at Type: The Fundamentals - Charles Martin, Ph.D.