He's in the Bible in the book of Revelations. The Bible is where we actually get "The Four Horsemen." At the End of Days, the Antichrist is supposed to be the one to step on the scene and take over the world and he's really, really evil. Most people don't include him in "The Four Horsemen" and prefer to use "Pestilence", but in this piece, seeing as how the person sitting on the lead horse is majestic looking and powerful, I'm inclined that the artist intended for them to be the antichrist.
Other interpretations view him as Conquest, representing the spread of Christianity. These interpretations do not view him as evil but instead as a force of justice. I think korintic likely meant for him to be that-- korintic's depictions of evil are usually grotesque and very corporeal, this depiction seems to have more of a holy quality to him. That being said, I'm not the artist so I can't speak to his intentions.
Conquest. War is the one with the fiery head and spears going through his body. Conquest is biblically the Rider of the White Horse, though in the West he is sometimes replaced with Pestilence, as white was associated with disease. Here is the embodiment of Conquest, symbolizing the subjugation of Humanity.
I always interpreted conquest as human greed and lust for power, spreading chaos through the nations, thus bringing forth war, famine, and ultimately pestilence and death that wipe out millions of lives.