The following points are important ones in creating any main character:
Character Name
There are many cool names but select the one that is definitive of the character. "Stanley" usually isn't knight in shining armor but the knight my have a "Stanley-esque" quality that gives him more depth. An interesting name is particularly important for the Protagonist and Antagonist. They should be equally catchy. Luke Skywalker versus Dennis Vader just doesn't sing.
Character's theme in one word
Just like the screenplay's theme, what is the character's theme? This can be your own personal "catchphrase" while when wondering what the character might do in any particular situation. Remembering the theme just might help you figure it out.
Age
How old is he or she? You must take several things into consideration: innocence, wisdom, puberty, debilitation, etc. Anything that hinders or helps your character will be reflective of his/her age.
Gender
Male or Female? Again, how will this point be detrimental or not in any given situation.
Appearance
How does the character present him/herself? An appearance that is the complete opposite of what the difficult undertaking calls for is always a good rule of thumb. (Superheroes don't count)
Defects (scars, or limps)
Any physical defects? Good for giving your character vulnerability and giving fodder to a backstory.
Marital status
Married? Single? Divorced? Widowed? (circle one) This highly affects personality. Anyone who is or was married knows this all too well.
Family
Does your character have a family? Does he/she like them? Are they a component in the story? And, if so, do they hold he/she back or provide support...or are they a liability?
Friends
Does your character have any friends? If so, what are they like? Defines what your character is like.
Religion
Not always important unless the story calls for it but if you want to dig deep for you own information it is good to know. With religions come cliches and, like or not, people will identify with that.
Occupation
What does your character do for a living? Again, this just might tell you and the audience what makes them tick.
Formal Education
Did your character go to school? How about college? PhD? Maybe the sixth grade was sufficient. This knowledge presents "book smarts".
Acquired Education
This knowledge presents "street smarts". Much more attractive to have someone who only finished the eighth grade reach CEO status. So, what knowledge does your character have from the guy in the empty refrigerator box behind the mission that no one else does?
Quirks
What peculiar behavior does your character have? Nail-biting? Twitching? This behavior could be representative of your character's flaw and that is a good thing.
Core Beliefs
What is most important to your character along the lines of ethics, spirituality, death, etc. The point here is to define how much depth your character has in making he/she appear more human.
Associate Objects
Maybe your character has a cane...a slingshot...a Zippo lighter...or chewing game. An associate object further defines your character. So what is it? We all have something.
Favorite Hobby
What does your character do in his/her spare time? Something like could tie directly into the storyline or give further depth of character. Tough cops who collect "My Little Pony" dolls is always a big winner. Imagine the possibilities.
Greatest Talent
What can your character do that rivals what he/she might come up against? Having a talent saves the day. Period.
Greatest Strength
This should focus more on the character's personality? What might other admire about how your character carries him/herself?
Greatest Weakness
What is your character's flaw? Again, more in depth if the flaw is a personality shortcoming. So, with that in mind, what is it that might keep your character from achieving what they want or need?
Greatest Fear
No matter how "together" your character appears to be they must have a fear. What is it? This could be the Achilles Heel that blocks an Protagonist or defeats an Antagonist.
Darkest Secret
We all have one. What's yours? What's your character's? This is another bit of information that plays well when providing a backstory for you screenplay. Also, a dark secret is going to dictate how a particular character acts.
After completing these "character points", you should have a pretty good idea as to what your character is like. If you did correctly, there will be a lot of you in the character. Write what you know!