In fiction most protagonists like most people are not complete loners. Interactions with their cohorts make up a good portion of novels, so creating these peers takes a bit of thought. What enables a real-life group to be innovative in business also makes for interesting interplay between the main character and their group. A peek inside of what helps real work groups to collaborate and solve problems maybe the key to creating the cohort that complements the unforgettable protagonist.
With all the current emphasis on collaborative thinking and collective knowledge in the workplace, you might assume assembling a large group of properly motivated people could solve almost any problem. You don’t really believe this do you? The larger the group is, the less each person is inclined to contribute. According to Fortune Magazine 4 to 5 is the magic number.  Wharton School of Business uses 5 to 6. Get beyond this and you will have social loafing, members who fail to contribute much or are kept from contributions due to the self-enforced conformity of large groups . Most people will then tend to follow the loudest voice that supports the status quo. Of course maintaining status quo not only limits creativity. It also makes a boring plot line.
The ideal size of the team depends on its goal, but teams larger than eight people fail to function efficiently.  In the same manner, a large number of well drawn auxiliary characters dilute attention to the struggles and triumphs of the main character. And they will confuse the readers to boot. Students studying literature keep lists of characters when reading epic novels to make enjoyment easier; not all readers are willing to do that.
In real situations, diverse groups are smarter and better at problem solving. This is particularly noticeable in the case of gender and ethnic diversity. Add females to a formerly all male group (and vice versa) and the collaborative IQ rises. Ethnic differences make viewpoint differences more acceptable because, oddly enough, people become more upset when a view that conflicts with theirs is proposed by someone that looks and acts like them, rather than someone obviously different.
This kind of attitude occurs in the fictional world also. Consider the difference between a foil and a doppelganger. Cervantes’ Don Quixote is tall, thin, and an impractical idealist, while his Sancho Panza, is short, fat and a realist. These differences in temperaments and appearance not only play the main character off of his side kick, but provide a range of resources so that they can assisting in helping each other get out of trouble.
However, the when the main character has an unnatural twin, a person who appears the same physically but is on the other side of the behavioral spectrum, the outcome is virtually bound to be tragic. It doesn’t matter whether the twin is an actual human, as in the Charles Dicken’s “Tale of Two Cities, a mythical doppelganger, as in Edgar Allen Poe’s “William Wilson,” or simply an illusion as in Fyodor Dotoevsky’s “The Double.” One (or sometimes both) of the identical appearing people are almost always doomed.
When you think about it perhaps it would help people doing research on successful work group successful to take a peek into successful main characters and their cohorts.
 Woolley, Anita. and Malone, Thomas. Defend Your Research: What Makes a Team Smarter? More Women, Harvard Business Review Magazine June, 2011.