We introduce our characters to our readers through dialogue. Dialogue combined with facial expression and body language indicates to readers who our characters are. In real life, this is how we get to know one another. We start interacting. Sometimes this goes well, sometimes it doesn't. Through dialogue, we decide if we like someone or not. This is also how our readers decide if they like our characters. As they listen to them and watch them interact with each other, they decide if these are good guys or bad guys or a combination. It's in our power to evoke positive or negative feelings in our readers for our characters through the dialogue we create for them.
Gloria Kempton, Dialogue, 2004