I'd swear I made this list before, but I can't find it.

• They have interesting back-stories.
• They have suffered deeply in a way that still affects them.
• They have pasts that are as important as their presents.
• They are complicated; they have dimensions and complex reactions.
• They could have the motto: "What you see is not necessarily what you get."
• They feel strongly about certain things, both positive and negative.
• They need and want things so badly that they strive to get them.
• They don't have their present life under control.
• They have as many flaws as they have strengths.
• They struggle to survive or thrive without burying themselves in angst.
• They have a variety of honest emotions that they can't avoid feeling.