The Greek notion of a hero basically says:  Heroism comes with great sacrifice (Odysseus, Hercules, etc).  The Greeks also gave birth to the notion that the hero is--by nature--unable to live among man and is by the same nature, both isolated and alienated.  A loner.

Then, there's our literary definition:  The principal character in a drama, novel, story, or narrative poem.  A protagonist.

A hero also possesses great bravery.  What's the definition of "brave?"  Resolute in facing odds.  Able to meet danger or endure pain without giving into fear.

What is "noble?"  Possessing very high or outstanding qualities.

Courage?  Mental or moral strength enabling one to venture, persevere and endure danger, fear, or difficulty firmly and resolutely.

Is a hero "smart?"  Does he have superior intellect?  What is "smart?"  Having or showing mental alertness and quickness of perception.  Resourcefulness.

Strength?  Does a hero have to be strong physically?  What is "strength?"  The quality to withstand force without breaking.   

A hero has all these qualities both in real life, and metaphorically.  But having these qualities isn't enough.  He must use them to help those who are less fortunate than himself.  True heroism is selfless and doesn't seek recognition.  A hero also realizes that but for his circumstances, he's no better or worse than the people he's trying to help.  He's one of us.

Clark Kent, Superman's alter ego is just a common man who doesn't seek recognition.  Bruce Wayne/Batman, the same thing.  Bruce Wayne is wealthy, but he's humble about it.

In a nutshell:  A hero says and does things ordinary people don't say and do.

It's one thing to talk about it, it's another thing to actually practice it!  A hero steps up to the plate when the situation warrants it.  He'll put himself in danger to help a person in trouble without regard for his own safety.  He's not reckless or suicidal, but his actions go beyond what "normal" people would do in tight situations.

It's important to realize your hero is only half of the equation!

In order for a hero to be a hero, he needs a person, thing, or situation to overcome.  Most of the time it's a person in the form of a villain.  This villain works in direct opposition to the hero.

What is a villain?  A person of uncouth mind and manners.  A boor.  He's also a person of depraved and malevolent character devoted to evil acts.  One who deliberately plots and does serious harm to others.

In simple terms:  He's the opposite of your hero.

***  Your villain must posses equal or higher skills than your hero. ***

ALL GOOD FICTION IS CENTERED AROUND CONFLICT:  It's the foundation that drives your story.

In real estate, it's location, location, location.  In fiction, it's conflict, conflict, conflict.

Your hero and villain are tools to create conflict in your story.

If your villain is shallow, foolish, or inept, your hero's job is too easy and you don't have "real" conflict.  The same could be said for your hero versus the villain.  But there's a difference:  The villain almost always has the upper hand as the hero generally doesn't know what the villain's master plan is.  A large part of telling your story revolves around your hero figuring out what the villain plans to do.   He must then form and implement his own plan to find and defeat the villain.

Just as your hero has some undesirable characteristics, your villain will have some admirable characteristics.  He's not all bad.  He has some good qualities.  Your villain might have a soft heart for animals, or be caring for a sick relative, or give money to charity.  Giving your villain at least one good quality makes him deeper and more interesting.

What is the role of your hero in the story?

A hero takes on a mission or assignment.  Let's call it "The Hero's Journey"

He has a goal:  To overcome or defeat the villain(s)  And it's never an easy journey.  There are obstacles and forces working in direct opposition to your hero's goal.  He may (and probably will at some point in the story) find himself at odds with other "good guys."  The villain isn't the only force working against him.  It may be his own inner demons, or someone he's close to (a betrayer) or something he's afraid of.

Remember, your hero has faults (character flaws) and they will play a role in how he sees the world.  Generally speaking, the hero is aware of his faults and weaknesses.  He doesn't deny having them, but he'll have to overcome them to prevail.

What is the role of your villain in the story?

He gives your hero a job.  The villain IS THE FOUNDATION for your story.  Without a villain and his "master plan," you don't have a story and your hero has no job -- he's in the unemployment line.

And often (but not always) your villain doesn't think of himself as the "bad guy."  From his perspective, he's the "good guy."  Terrorists are classic examples of this.  One man's terrorist is another man's freedom fighter.  Your villain may believe he's acting honorably, but your reader will know otherwise.  Often the villain doesn't care about the consequences of his actions, that's why he's a villain.  And it makes the hero's job all the tougher.

So it's vitally important you understand your villain, both inside and out, and you must know his motivations.  What makes him tick?  Why is he doing the things he's doing?  Because...

 ***  Your villain drives the story ***

This can't be stressed enough:  Without him, you have no story.

As you plot and write your story, an important question arises:

HOW BAD CAN YOUR GOOD GUY BE?

There's no concrete answer to this question except that your hero must be distinguishable from your villain by what's in his heart.

Your hero may believe he's acting dishonorably, but your reader will know otherwise.  At one point in your story, your hero will ponder an important question:

When is life ever as simple as book of rules?

How far can he bend those rules?  Does the end justify the means?  If the stakes are high enough, can he act outside the law or what society considers acceptable?  Theft?  Deceit?  Even torture? 

It's a fine line to walk, but it gives your hero depth.  The fact that's he's asking himself these questions speaks volumes about his character.

How can your hero play by the rules and expect to win if his opponent doesn't?

Can you imagine the one sided routing of a sporting event where only one team had to follow the rules?  The game would be boring and predicable -- the kiss of death in fiction!

***  The villain will force your hero to break the rules. ***

This should (and will) create conflict within your hero.  He won't like doing it, but he'll realize it's a necessary evil.  It may even lead to your hero finding himself in greater danger because he's initially reluctant to break the rules. 

As brutal as it sounds,  YOU MUST TORMENT YOUR HERO!  Both mentally and physically.  Remember, "The Hero's Journey" is never easy.  He must overcome obstacles to make your story interesting.  There's rarely smooth sailing for your hero.

The movie "Fugitive" is a good example of a hero overcoming obstacles.  It's believable.  Well, maybe surviving the leap from the dam is a little farfetched...

A couple of Don'ts

Don't recreate Superman.  Your hero doesn't dodge bullets or avoid being (seriously) injured.  He bleeds just like the rest of us.  Hollywood often gets this wrong.  His injuries may be so serious that his goal could be in jeopardy.  A flesh wound is one thing, a bullet through the rotator cuff of the shoulder puts your hero out of commission.  Period.  He doesn't climb a chain link fence or continue hand to hand combat with that type of wound.  It doesn't happen.  So be careful with your hero's injuries. 

Don't deliver a "white knight" at the end to bail your hero out of a tight or life-threatening situation.  Generally speaking (and there are exceptions) A hero solves his own problems.  He may get some assistance, but he does it himself. 

Don't cheat your reader.  Have you ever read a book where you say to yourself, "Come on... that was lame."  It's usually the result of lazy writing. Or an author cutting plot corners to make a deadline.  Just as your "Hero's Journey" isn't easy, neither is your job as an author.  Plotting can be the most difficult part of writing.  My plots are character driven, not the reverse.  With thrillers, it's not uncommon to spend as much time potting as writing. 

Don't let your hero "preach to the choir."  Unless you write political thrillers, be careful about using your hero to advance your political, environmental, or spiritual beliefs.  Your readers will see right through it.  It will bore them to tears at best, and stop them from reading your novel at worst.  And they'll be quite hesitant to buy your next book.  You're asking people to take their hard earned cash and buy your book, so you should deliver the goods without strings attached!  Your job is to entertain your reader, not sway their political opinions.  Your way of looking at the world will manifest itself through the actions of your hero, not his political views 

And a personal note:

Don't give up.  Ever.  Everything you need to succeed as a author is available at writers conferences, like ThrillerFest in New York City. Your goal is to constantly improve your craft.  Good writing gets noticed.  If you work hard and refine your skills, someday an agent or editor will be reading your manuscript and say, "Wow, this is really good!"