It is unknown how the Elsians were founded or who founded the Elsians. At some point in Archian history however, a notorious bender named Shizu killed nearly a thousand people with bloodbending for no reason and because "he was bored."
Later, some other benders followed in Shizu's footsteps and began to commit mass genocides and murders across the globe because they either wanted to or that they were bored. Some even went as far as slitting throats of the men and children, and raping the women. This act led to the extreme hatred of the Elsians, but that didn't stop them from continuing to commit mass murders and massive scaled genocides.
After that event in history, all other documents of Elsians in the early ages were lost in history, never to be found again.
Elsians are wicked and insane people. Most of them are crazed and are mentally unstable. They love to rape woman because they consider them their "prizes" in war and they love to slit and murder people because they "love to see the blood flow like water." Some even go as far as cannibalizing because they consider it "an act of God and only those with the true faith will perform the act."
Elsians follow something that is known as the "Wicked Code."
That's how we roll! We come and we kill! We destroy and we maul! We slay what we wish and we claim what we want! We are the Elsians, and we will strive to cover the world in blood as our victims fall to the bloodied ground beneath them
Overall, they are wicked and very insane individuals, who wish to kill and will do so to anyone they want.