Readers may be drawn to the impassioned, spirited, exciting and mercurial hero figure. In real life we often find of these people over-emotional, high-strung, frenzied and hot-tempered. So this kind of protagonist needs a balancing factor. A good place to find the appropriate personality for the mentor or sidekick to assists your hero is in research on creativity in business. Creativity is no long the domain of eccentric inventors, impractical daydreamers, and those living in garrets on the edge of poverty. In the business community it has become a buzzword for bolstering a faltering company. But the wise sociologist realizes that creativity is strongly related to non-conformity. And, non-conformists rub many people the wrong way. The latest trend in innovation research tries to define the various creative styles that will support each other (and bolster the company’s bottom line). These are excellent resources to use as the basis of your characters.
For example, Kirton Adaption-Innovation Inventory describes Adaption and Innovation as styles of creativity. However, at close examination the different styles are related to levels of conformity/non-conformity. This inventory scores people on a continuum ranging from working with the system to challenging the system. 
The Spontaneous approach is marked by freedom from constraint and traditions. It is an ADHD style that focuses on many goals at once, impatiently jumping from one thing to the other–the feeling approach to coming up with solutions to the major conflict in your story. (Consider the similarities with the ill-prepared character on a mission to right an injustice.)
The Conceptual approach is centered on formulating new ideas, different alternatives, innovative concepts, and creating an overall plan. This is the problem solving style of the thinking person. (Think of the highly intelligent, but eccentric private detective.)
The Normative approach requires putting new ideas into a familiar context, based on past experiences. People employing this approach need to know the consequences beforehand. This play-it-safe style is mostly conformist. These people follow rather than lead when it comes to original ideas, but these are the kind of people that end up in leadership positions. (For example, the police chief who just can’t see the possible answers that the private detective can in many mystery novels.)
The Methodical approach is not really creative at all but focused on proven solutions and creating order. However, a spontaneous or conceptual person people can become methodical and adopt a step-by-step procedure when it comes to testing their novel ideas. Or you can simply add a methodical sidekick with the detailed know-how to make the hero’s far out idea work.
Fahden’s & Namakkal’s research has led to profiles that identifies people as the Creator, who invents with the new idea, the Advancer who recognizes this far out idea as a possible solution, the Refiner who methodically figures out what the consequences are going to be, and finally the Executor who pays attention to all the details.  This group seems to work as well in producing new products in real life as it does in fiction for the elite criminals involved in a high-stakes heist or the core group intent on carrying out some covert activity.
No one is purely creative or purely uncreative, so no one fits completely into any category. Most people use all of these approaches at one time or the other when faced with the “major conflict,” but they show a definite preference of one type of approach. So feel free to have your protagonist switch their approach occasionally when it makes sense. In fact, this would be a good idea for all major characters, even your antagonist.