Specifically, I want to know who this person is.

Here are some line by line comments:

He surveyed his surroundings with an admonishing eye.
Some things simply require two people. In order to admonish someone, you need someone to admonish. With the king now dead, your MC is all alone and thus he cannot admonish anyone else.

Before him lay the once great king of a new land, but now… a smoldering pile of ash.
This is the line I thought was nice.

A man, who once almost took his life, was just killed with the greatest of ease.
This is clumsy. It needs to be rephrased.

Retreating his hand back to himself and forming it into a fist he looked.

This would benefit from being shorter, and more concise: "He pulled his hand back, forming it into a fist." Also, ask yourself why this line is here? What purpose does it serve? I see no further indication that balling his hand into a fist is important to the story. Make it mean something, or consider taking it out. As with building a car engine, good writing should include no parts that are not useful.

It was now black as night.
What was "it"? His fist? Be specific.

He had almost lost this duel, but by summoning power through an ancient enchantment, his power increased by ten fold.
This line indicates to me that you started the story in the wrong spot. We obviously need to know something more about who this is and the sort of power he wields in order to hook into, and care about, this character.

Only two (two what?) had called upon the spell before, and they died minutes after doing so. (How does he know?) But he, would not, he would become supreme overlord of the land. (clumsy. Need to rephrase because the gramatical structure of the sentence is off.

With a swipe of anger he reached down into his well of power, and began to grow mightier.
Anger doesn't swipe. Anger should be referred to more like energy, thus it can surge... but it takes a body part or a tool to make a swiping motion.

Any first line that could be rephrased to:

"They looked at the setting."