An (In)Sufficient Explanation

Ari - Phlegmatic
"A phlegmatic person is calm and unemotional....They are very consistent, relaxed, rational, curious, and observant, making them good administrators and diplomats."

Ben - Choleric
"A person who is choleric is a doer and a leader. They have a lot of ambition, energy, and passion, and try to instill it in others."

Will - Sanguine
"A person who is sanguine is generally arrogant, cocky, indulgent, and confident. He/She 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."

Zach - Melancholic
"Often very kind and considerate, melancholics can be highly creative - as in poetry and art - but also can become overly pre-occupied with the tragedy and cruelty in the world, thus becoming depressed."

From http://en.wikipedia.org/wiki/Four_temperaments.