This is often seen in fantasy fiction. The Chosen One. So use it. Go with it. And here is a guideline on how to do that.
Make them male
Just going to put that out there. And often white. Make them a young, white, male.
Farmboy or lowly servant
Make them start from simple beginnings. It is the contrast. Simple beginnings and then conquers the Big Bad. How? Wow! It is amazing that someone who started to simply could end up conquering the Big Bad. I know I am amazed.
Secretly royalty
This is a twist you can add. He is just a farm boy but he is Secretly the heir to the throne. No one will see that coming.
Mentor
You need some wise old mentor. Possibly a wizard. Who Knows things, man, he knows things. And he will train your farm boy into the hero you always wanted. Let’s face it farm boys lack the skills to fight the Big Bad. They have other skills. Like farming and raising animals. You need some sort of leap from farm boy to hero and your mentor can bring it on!
Perfection
Make your hero really Good. Not good but Good. Make them selfless, kind, and heroic. I mean how can you conquer Evil, if you are not Good. Am I right? The one flaw you can permit your character to have is self-doubt. About the quest. About being Chosen. About what to do. That is what the mentor and faithful sidekick are there for. To help with this overwhelming doubt.
Prophecy
They are Chosen, man. You need some sort of prophecy that explains how they could, if they try, conquer the Big Bad. But if they fail the world will plummet into darkness and despair. Or end.
Create obstacles
Create obstacles that only he can resolve because he is Chosen. Also, these can align with the prophecy and his massive goodness.
Faithful sidekick
This really jumps up the game here. Add in a character who is exceptionally loyal to your protagonist. And follows him everywhere. But has no exceptional skills. He is just there to keep your protagonist on ‘the path’. And to make sure he doesn’t ‘doubt himself’. I’d then randomly kill him off to spice things up.
Add all these in and it is the perfect Epic Fantasy. You’re welcome.
But I have no experience with Epic fantasy except an excessively long story I wrote when I was 18 or so. So do as you will, and if you do, make it EPIC. And you have to have some of these in your Epic fantasy to make it Epicly Epic. So pick and choose and put a wee twist on it. Because Epic fantasy is a blast to read.
Other really helpful advice
When to kill a character
What pets to put into your fantasy
How to get out of a stuck scene
The Wyrd 