Ouroboros is a large and largely unknown terrorist organization in Sternbild City.
It is currently unknown how long they have been operating, but Maverick made a deal with the organization to get a steady supply of villains for Hero TV, in exchange for the Emily Brooks's and Barnaby Brooks's technology. This would mean that they have been active at least since early in Hero TV 's history.
From what Kriem says the organization is larger than anyone believes. It is also unclear how powerful Ouroboros really is, but is hinted that its influence is quite enormous in scale.
It would seem Maverick has command over a small, yet substantial fraction of the organization, given he's not only manged to constantly supply criminals for Hero TV over the years but also had men on hand to help him distract Kotetsu so he could kidnap and kill Samantha Taylor.
It is also possible Ouroboros has some connections in the government that allow them to get their thugs out of jail for repeated use.
During the epilogue a local kid, while buying Barnaby Brooks Jr.'s and Wild Tiger's hero cards, drops his dollar in a puddle and the head of Justice is replaced by Ouroboros's symbol. This would imply they've infiltrated the ruling government of Sternbild.
Ouroboros's symbol is a stylized Ouroboros releasing its tail, with a spade for an eye and with a sword through its body. The top half of the snake and the sword are black, while the spade is red and the bottom half of the snake is white. Inside the circle of the snake's body are two unknown words.
The Ouroboros is an ancient symbol depicting a serpent or dragon eating its own tail. Originating in Ancient Egyptian iconography, the Ouroboros entered western tradition via Greek magical tradition and was adopted as a symbol in Gnosticism and Hermeticism, and most notably in Alchemy. Via medieval Alchemical tradition, the symbol entered Renaissance magic and modern symbolism, often taken to symbolize introspection, the eternal return or cyclicality, especially in the sense of something constantly re-creating itself. It also represents the infinite cycle of nature's endless creation and destruction, life and death.
All of Ouroboros's known members have at least one tattoo of the organization's symbol somewhere on their bodies. Jake Martinez and Kriem each had multiple Ouroboros tattoos. Kriem had two on her left shoulder, and Jake had one on each shoulder, one on his left bicep, and two on the left side of his neck above his collarbone.