In an Independent article about the drama "Christopher and His Kind," actor Matt Smith talks about figuring out how to play the role of Christopher Isherwood (pictured). Isherwood's long term partner told him that one of Isherwood's most memorable qualities was the fact that he was very polite.
Smith says, "I wrote it down..'it's about manners and lust'; and from that I sort of built upwards."
That could also be a interesting way for a writer to build up a character: what two words are the most essential? Finding them probably is a matter of intuition rather than analysis.
I just tried it for the protagonist of the script I'm writing at the moment, and what came up was "justice and control." Since he's a criminal, "justice" might seem a strange choice but for him it's really about what he considers right and wrong; and although he initially comes across as easy-going and genial, his mission is to be in control even though he's facing the toughest challenge to any control freak: death.
It could be an interesting exercise to do with a character you are creating--or, if you're really brave, with your own life.
(If you'd like support for setting and achieving your writing goal, join my online mentoring program, the Writing Breakthrough Strategy Program --details at www.jurgenwolff.com)