Warforged

The warforged lay dormant for a long time, but have since returned to the world of West Marches.

History
It's been theorized that the Cataclysm was caused by a great war on the continent, for which these sapient, autonomous constructs may have been forged. Whatever their purpose, they fell into neglect and disrepair following that event, the forges that once constructed their minds and bodies lost to time and the jungle, becoming the homes and lairs of all manner of dangerous creatures.

Frontier Forge
One such forge became the lair of a beast whose mere presence threatened the nearby town of New Gork through the corrosive radiance it spread to its surroundings. A party of adventurers from that town sought out and defeated the creature in 2324, during season 3, lifting the corruption and allowing the heart of the forge to beat anew.

The Frontier Forge is currently the only known active forge on the continent, having first produced Dawn, now New Gork's Head of Defense, and Shortstop Trace, a mysterious figure who appears to have taken the area around the Forge as his own domain. Additional warforged aren't conscripted to Shortstop's cause, whatever it may be, but he gives each one a choice: stay and join him, or leave and forever face the consequences of trespassing on his domain.

Wrongforged
Another forge was discovered in early 2345, during season 4, which produced hostile creatures that seemed part organic and part construct, made of metal and living wood. These "wrongforged," as they were called, were led by instances of the self-replicating entity who called themselves the Artificer and who identified their goal as the end of all life. Through the collapse of two Bags of Holding, an instance of the Artificer was shunted to the Astral Plane, where it's assumed to have continued replicating. The forge itself was destroyed and no longer poses threat.

Character Creation
Although the Frontier Forge is the only known active forge, there might be others that have become active again in recent years, or there could be warforged that survived the Cataclysm in dormant state and have only recently awoken... Please discuss any such potential backstory with a DM beforehand! Do note that no player characters, including pre-Cataclysm warforged, will have memories of things before the Cataclysm.