Two sides of the same coin

"She wears strength and darkness equally well, the girl as always been half goddess, half hell." ~Nikita Gill

It's important that when creating a character that you give them two sides; one that they become, and one that they overcome.  

"A mess of beautiful contradictions make her whole, she wears fire for skin but a storm lives in her soul." ~Nikita Gill

Characters, like real people, have more then one side. Look at your best friend, sure they're an amazing human being, but have you ever been afraid to make them angry? Maybe they're as punk as you can get but like to cry over sappy movies. Everyone has a side that you wouldn't expect when you first meet them. Remember, your readers aren't Sherlock. They can't tell your character's every habit by the type of hat he wears. 

You don't have to introduce readers to the other side of your character early on, It can even be introduced as late as the last chapter. 

Lets say your character is an Assassin trained from the age of six to kill without question. She follows orders without a second thought and always gets the job done. Then as it always does, something happens and she ends up helping your protagonist on their quest. We'll name them Arias and Nolan for simplicity's sake. Now Arias (the assassin) is always very cold and harsh. She never says more then necessary and hates physical contact. For the past two weeks they've fought together, Nolan (your protagonist) has been trying to get Arias to open up, he wants to learn something about her. Arias however has no intention of letting that happen. So a few more days past and suddenly Arias and Nolan need a place to lay low. Arias grudgingly suggest they go to the home of an old friend of her (she has friends ok? not all assassins are loners) and Nolan agrees. Now Nolan, like most of us, is probably expecting a grungy, smelly, pigsty, with an mean looking guy as their roomate. When in reality Arias takes him to a quant little cottage smelling of pies and cookies packed with four kids and their mum. After getting over his surprise Nolan expects Arias to be annoyed with the kids, cause why would an antisocial assassin like kids climbing all over her? Turns out Arias LOVES kids. She plays with them, tells them stories, makes them laugh, the whole shebang. 

That's the other side. Everyone expects Arias to be cold, hard, and just nice enough to be likable. But Arias is human so she has hidden interests. 

Did you care more for Arias before you knew she loved kids? Or after?

Even Marvel's Loki Laufeyson has two sides. One side is manipulative, power hungry, and a bit of a butt. His other side however cares deeply about his family, his honor, and his people. It's that other side that connects us to him on an emotional level.

Wether they overcome one side and become another, or are simply able switch back and forth. Giving your character another side will definitely help create an emotional connection for your readers.