What makes any hero or heroine "epic?"
Many of our favorite fictional characters are larger-than-life. They are lucky in ways we'd never be, and they always seem to suffer through a lot more than any of us here in the real world ever could. Unlike the reluctant hero/heroine who has fears and doubts to overcome, those epic personalities don't suffer from such misgivings--they know their business.
It's not unusual for the epic hero to have been through a lot before your story begins. That's why they know how to do some of those really cool things. Having the skill to kill your way through dozens of henchmen before you can ruin the villain's day means that somehow, somewhere, your hero/heroine got enough experience (possibly the hard way) to do it. They know how to overcome long odds, even if that means breaking a few heads.
Skill and savoir-faire are only part of that winning recipe. It takes more than a sexy smile to defeat the forces of darkness. Your average Bad Guy knows what they want, that's why they're doing it. Being up to no good is more than planning a crime or directing your underlings to make it work. Villains must be prepared to lie, cheat, steal, or kill when there is no other way. It's a well-known fact that those pesky do-gooders don't go quietly. They need to be--well--incentivized to see things your way or die while fleeing in terror.
Sometimes, the fate of the human race is not at stake. Saving the world is fine and well for those who do it--but--let's be real for a second: the world doesn't always need to be saved. Sometimes, it's just a matter of morality and/or ethics that confound your heroes and heroines. Who lives and who dies? Asnwer that and you've got the basis for a conflict worthy of any protagonist.
There is one ticklish point to consider. The epic hero who is capable of great things must also be strong enough to live with what they did. Yes, the Bad Guy is defeated--at what cost? How many innocent lives were lost to achieve that goal? Was "truth" one of those casualties? Maybe, it's better if the general public doesn't know about...that. The thing you had to do. As terrible as it was, they don't really need to know...do they?
That's why epic heroes and heroines are so hard to write, even when you know how the story ends.