A good way to help bring your characters to life and to establish a back story for them is to develop answers to a set of questions about them.
Where is your character from?
How old is your character?
What is your character called?
What does your character look like?
What kind of childhood did your character have?
What does your character do for a living?
How does your character deal with conflict and change?
Who else is in your character’s life?
How does your character deal with conflict and change?
What is your character’s goal or motivation in this story?