There is far more to this world than we know, and we humans are only a small part of it
While we may be the most populous, we are far from the strongest creatures, and our petty quibbling over cultural differences, world views and politics don't even rate among the true dangers we unknowingly face on a regular basis.
Every day humans face threats from other beings intent on subjugating us, using us or simply feeding on us--beings we believe to be myths or legends or are blissfully unaware of at all. How do we defend ourselves from such things?
Guardians are humanity's defense against all that would harm it, constantly fighting in the shadows of our world. They also act as our envoys into these realms, maintaining peace when possible.
Throughout our young history, humans have been exposed to beings from other planes of existence--powerful creatures that have often sought to enslave us and rule us as would-be deities or even gods. Not all of them have been harmful.
Some have even proved beneficent or helpful, but most are power-hungry. Every ancient race of humans has dealt with them and most survive and move along, changing their ideology. Somewhere in the background were the Guardians.
Long before humans walked the Earth other races of creatures existed, and they were less than thrilled with our sudden and successful appearance. Hundreds of races of Fae, or fairies, view us a plague to be avoided, while hundreds of others would still rather see us eliminated altogether. Other creatures see us simply as food or even a way to carry on their bloodlines. Still other dangers have evolved alongside us, in fact, evolving from us. Yet we still thrived because somewhere in the background were the Guardians.
Who are the Guardians? No one is sure. We don't even know how many of them there are, but these Chronicles are the tales of the oldest one--Diomedes Tydides, King of Argos and hero of the War of the Epigoni and the Trojan War. For over three thousand years he has fought in that shadowy world to protect us, relying on strength and power granted by the deity known to him as Athena. For us he has waded where others would not and fought things no man should have to face. And so far he has never failed...