Humoresque

Hippocrates believed moods and behaviors were caused by the balance of four bodily fluids (called humors): blood, yellow bile, black bile, phlegm. During the Renaissance, Shakespeare and other authors based characters on the four humors or temperaments. It's good to have a balance in real life, but for characters it's good to be unbalanced :-)

Come up with some characters based on the four humors. Set them in a situation together and see what happens.

Sanguine (blood, cheerful)

A sanguine person is generally light-hearted, fun-loving, a people person, loves to entertain, spontaneous, leadership abilities, and confident. However they can be arrogant, cocky, and indulgent. They can be day-dreamy and off-task to the point of not accomplishing anything and can be impulsive, possibly acting on whims in an unpredictable fashion.

The temperament is associated with the season of spring, the qualities of warm and moist, the element of air. Various modern equivalents are: artisan, improvisor, artistic, innovative, changeable.

Synonyms: cheerful, confident, optimistic, assured, hopeful, buoyant, in good heart

Choleric (yellow bile, enthusiastic)

A choleric person is a doer. They have a lot of ambition, energy, and passion, and try to instill it in others. They can dominate people of other temperaments, especially phlegmatic types. Many great charismatic military and political figures were cholerics. On the negative side, they are easily angered, bad-tempered, mean-spirited, suspicious and angry.

The temperament is associated with the season of summer, the qualities of warm and dry, and the element of fire. Various modern equivalents are: idealist, catalyst, religious, doctrinaire, inspired.

Synonyms: irate, testy, hot-tempered, fiery, irritable, quarrelsome

Melancholic (black bile, somber)

A melancholic person is a thoughtful ponderer. Often very kind and considerate, melancholics can be highly creative – as in poetry and art - but can become overly pre-occupied with the tragedy and cruelty in the world, thus becoming depressed. A melancholic is also often a perfectionist. This often results in being unsatisfied with one's own artistic or creative works and always pointing out to themselves what could and should be improved.

The temperament is associated with the season of autumn, the qualities of cold and dry, and the element of earth. Various modern equivalents are: guardian, stabilizer, economic, traditional, industrious.

Synonyms: languid, spiritless, gloomy

Phlegmatic (phlegm, calm)

A phlegmatic person is calm and unemotional. While phlegmatics are generally self-content and kind, their shy personality can often inhibit enthusiasm in others and make themselves lazy and resistant to change. They are very consistent, relaxed, rational, curious, and observant, making them good administrators and diplomats. Like the sanguine personality, the phlegmatic has many friends. However the phlegmatic is more reliable and compassionate; these characteristics typically make the phlegmatic a more dependable friend.

The temperament is associated with the season of winter, the qualities of cold and moist, and the element of water. Various modern equivalents are: rational, theorist, theoretic, skeptical, curious.

Synonyms: unemotional, indifferent, cold, heavy, dull, sluggish, matter-of-fact, placid, stoical, lethargic, bovine, apathetic, frigid, lymphatic, listless, impassive, stolid, unfeeling, undemonstrative

There's a chart that categorizes the traits and strengths and weaknesses of each:

If you'd like to see the mixture of humors in your character (or yourself) there's a personality test.

The Divided Kingdom by Rupert Thomson is about a world where people are isolated into quarters by personality type. I'm seeing some inherent conflict there in a land filled with leaders but no followers and thinkers but no doers.