I believe every character a person makes is a little bit of them. Maybe just a tiny detail - but in some way, from heroes all the way through to villains - our characters reflect who we are.
I recently started watching Season 2 of Marco Polo, and the first two episodes begin with a pretty big bang. This bang inspired me to write an article. This article will have spoilers of a sort, but I'll keep the details out of it. The keen observer will be able to figure out what's happening, so if you care about that sort of thing, turn away now.
I'm also going to make random conjecture, and suggest possible endings to the show without having seen the end of the Season, so take everything I say about the show's events with a grain of salt.
I'll also be throwing around the term good a hell of a lot. By good, I don't mean the opposite of evil. I mean "well-rounded", "interesting", "engaging", "dramatic", "exciting"... Basically, I mean a character that you'd want to read about. You may hate who they are, but not how they're told, or the story they force into existence. By good, I am assuming that you want your roleplaying characters to exemplify the traits I mentioned above. If you don't, ignore everything I'm about to say...
Good Characters Have Motivations
Every good character I know has something they want. More to, they have a reason why they want that thing. This goal and reason together forms their motivation. A motivation is more than just a base want. It is everything that surrounds the want that makes the want interesting.
Let's look at two motivations from Marco Polo:
Kublai Khan wants to be a great ruler, but mainly he wants to be a great ruler so that he's considered better than Ghengis Khan, the greatest Mongolian ruler ever. Many people want to be the head-honcho in the series, but it is because of Kublai's obsession that he is so compelling.
Kaidu wants to be Khan to prove that the Mongol way is right. He believes that Ghengis Khan's original message of expansion has been deformed and broken by Kublai's reaching, and wants to, in his eyes, redeem the Mongols. He hates the weakness that he perceives comes from trying to be Emperor of all Mongolia and China.
Here we can see two very similar goals, yet vastly different motivations. Already, the keen GM should be thinking of future plots where these two characters could come to blows...
Good Characters Have Limits
Now, character motivations aren't anything new - we've had roleplaying games that have mechanised motivations for years now, and to very good effect. They work well, but I believe for true dramatic gaming, they need to be pushed. Motivations need to be tested, otherwise the game is just a script.
Does Kaidu kill Kublai to take the throne?
Without limits, of coarse he does. If he has the option, the means, or the chance, he must kill him. It would fulfill his motivation, and he'd win.
However, what makes the character's so compelling - and what can make your characters so compelling - is the limits that are placed on them, by themselves. The characters know what they can and cannot do to achieve their goals.
Kublai Khan has no qualms with killing Kaidu for threatening his throne... He'd even enjoy it, and has been hoping to cross blades with him for some time. However, he's limited by the law. He knows he can't turn down a challenge given within the law, so must accept to undergo an election of sorts. This chafes at him, because even though he has legitemacy, he lacks massively in diplomacy. Kublai, with the greater army, and the greater claim to the throne, fears for his position because his weaknesses can be exploited. This will lead him to compromises that he might not be happy about...
Kaidu has diplomacy. He also has the backing of the law (see above). He knows that Kublai's armies are meaningless if he fights him in an election. But that means he has to sway lots of other chieftains, many of whom are loyal to Kublai. This brings together a great scene, in Season 2 Episode 2. I won't spoil it, but from it we learn that Kaidu has a second manifestation of his core motivation - he believes acting like Ghengis is more important than being Khan. Whether this works out for him or not, is yet to be seen...
From these limits, we get tension. Characters must play to certain rules which dictate their actions and their methods of attaining their goals and achieving their motivations. The best limits are those that make their motivations harder to attain, which leads us to...
Good Characters Make Choices
The moment a character has to make the choice between their motivation and their limits. Does the character accept that their limits are there for a reason, or do they break past them and trust that the ends justify the means?
Kaidu, in the example above, chooses to stick to his limits. He'll figure out another way to achieve his motivation, even if he makes it harder for himself along the way. He's a man of honour or principals, regardless of the morality or righteousness of his motivation. He plays by the rules he's set himself. In old-school terms, he'd be Lawful.
Kublai, on the other hand, faced with several threats to his throne, chooses to dance around his limits. At first, he claims a certain act is unthinkable. Then, he knows he must do it. Then he is convinced against it... Just as we're certain he's turned the other cheek he... Well, I won't spoil this one either. However, the final scene of Season 2 Episode 2 is so perfectly on-point for interesting choices that I urge you to watch that episode, even if you don't care about the rest of the show.
The point is, Kublai isn't certain that his limits are set in stone. He's willing to listen to council, and to change and bend as a person to achieve his goals. Therefore, the drama becomes about what he will decide to do. What choices will he decide to make? He's what we'd call Chaotic.
The main point I'm trying to make, for GMs, is that the best moments of the show - and the best moments for your game if you care about personal and characterful drama - are when you give a player the chance to achieve their character's goals... But then you test their limits. Do they take the leap and risk who they are to become what they want? Or do they sacrifice their dreams to hold firm to their morals and inner voice?
THAT is what I've learned from watching Marco Polo...