system
Given the following post, respond as if you're commenting on Reddit:
human
[Doom] What's so special about the Doom Slayer?

He is supposed to be every demon's nightmare, but basically all he has is some guns and a lot of ammo?

(Doom Eternal not included, where he gets the cool sword). 

What makes him so different than let's say the Punisher from Marvel comics?
gpt
> In the first age, in the first battle, when the shadows first lengthened, one stood. Burned by the embers of Armageddon, his soul blistered by the fires of Hell and tainted beyond ascension, he chose the path of perpetual torment. In his ravenous hatred he found no peace; and with boiling blood he scoured the Umbral Plains seeking vengeance against the dark lords who had wronged him. **He wore the crown of the Night Sentinels,** and those that tasted the bite of his sword named him... the Doom Slayer.

-- *The Slayer's Testament I*

> And in his conquest against the blackened souls of the doomed, his prowess was shown. In his crusade, **the seraphim bestowed upon him terrible power and speed,** and with his might he crushed the obsidian pillars of the Blood Temples. He set forth without pity upon the beasts of the nine circles. Unbreakable, incorruptible, unyielding, the Doom Slayer sought to end the dominion of the dark realm.

-- *The Slayer's Testament III*

> The age of his reckoning was uncounted. The scribes carved his name deep in the tablets of Hell across eons, and each battle etched terror in the hearts of the demons. They knew he would come, as he always had, as he always will, to feast on the blood of the wicked. **For he alone could draw strength from his fallen foes, and ever his power grew, swift and unrelenting.**

-- *The Slayer's Testament IV*

Summary: he's a fallen knight/angel who used to belong a group of holy protectors, who can absorb power from the demons he kills.