Kur is considered the first ever dragon, an ancient Sumerian cryptid that ruled all other cryptids.
According to V.V. Argost, the creature known as Kur was ancient before human civilizations arose. Kur had rampaged across the ancient world unopposed for years, until the warrior-king Gilgamesh challenged his might. Travelling across the known world, Gilgamesh discovered the Legion of Garuda, and with their help he defeated Kur and banished his spirit. An account of this battle was recorded in The Epic of Gilgamesh. Some time before his defeat, a part of Kur's essence was used to create the Naga relic. Afterwards, Kur's spirit clanged on to the Kur Stone to keep himself alive. The Kur Stone lay hidden for millennia until Solomon and Drew Saturday recovered it. Upon being found, Kur's essence leaped from the stone into Drew's unborn baby Zak, making Zak Saturday his reincarnation.
Main article: Zak's Power
Kur was rumored as the legendary cryptid that could lead all other cryptids in the war that would destroy humanity. This limitless power is why it is important for the Secret Scientists keep out of the wrong hands.
When it was found out that Zak was Kur, the Saturdays were even more concerned about the danger he could put them all into. Zak was especially worried that the Kur part of him might actually want him to lead the war.
In The Thousand Eyes of Ahuizotl, Zak couldn't influence Ahuizotl; because of the creature's ability to steal eyes he was wearing a mask, therefore couldn't see. Eventually, Zak discovered he didn't need to see the cryptids to use his power with them. With this, he was able to send the cryptid back to rest.
In Life in the Underground, Zak was able to contact the Jishin-uwo to help save Ulraj, Wadi, and himself, from suffocating by calling for help with cryptid telepathy. He then communicated with all the other cryptids to assure them that the new Kur wasn't evil and they had no reason to be afraid. He also said, he would call them if he needed them.
In War of the Cryptids, Zak was shown to have formed and controlled a whole army of cryptids fighting all over the world at once. He also was able to overpower Argost's influence on some flying cryptids with his, thanks to having more experience with his power. He could even communicate with other cryptids around the world with his mind.
The Saturdays learn that in order to drive out the spirit of Kur, they have to use the Flute of Gilgamesh that the Nagas stole centuries ago. It turns out that the Nagas have a good reason to steal it; if you drive the spirit out of the person with the Flute, you will kill it. But Zak IS Kur, not someone possessed, so if the ceremony is performed you would kill Zak as well. This proves that Zak truly is Kur. (In an interview with the writer of the series, he revealed that Zak really is "the reincarnation of Kur.")
V.V Argost took in Zak's powers, and along with the Monday power he already had, causing a reaction with Anti-Matter and Matter that sucked him out of existence. Kur is again gone, possibly forever now, once and for all.
In the Show
Throughout the course of the show, The Saturdays tried to find Kur, determined to stop Argost from finding and releasing the cryptid, as it could be used to control every other cryptid in the world. Since Zak had been born the same year the Kur stone was found, it was believed that Zak could be the only one who could stop Kur if it was ever released, as Zak's powers allowed him to influence cryptids and use them to his control. In the episode, Kur Rising, after an intense battle with V.V. Argost, "Kur" is defeated by Zak, but when Doyle shows up and activates the Naga Kur Detector, instead of it glowing near the creature thought to be Kur, it glowed when it came near Zak, thus, it made Zak's eyes glow orange with a symbol that appears to be the letter c with a line connecting to a circle that is shown on the Kur Stone at the beginning of Kur Rising, revealing that Zak was Kur the whole time.
Rani Nagi and her Naga returned in the season two premiere "Kur". After it was revealed that Zak is Kur, the Nagas sought him out, calling him their master. Rani attempted to convince Zak to tap into his inner Kur and lead cryptids in a war against humanity, and thus "a new era." Her attempt was interrupted by the timely arrival of the rest of the family and after a rough battle, they saved Zak and escaped. However, the Naga's had already succeeded in having Zak's power call summon the most vicious cryptids from around the world in a battle against humans, with Rani and her Nagas leading it in the name of Kur.
It was eventually learned that the Kur Stone Doc and Drew discovered before Zak's birth contained Kur's essence. During the accident when it was uncovered, the energy left the stone and found a new form as a host, namely, the unborn Zak, because as Rani Nagi, said, it was a much more dangerous form as the bridge between the worlds of humans and cryptids. Despite the Saturdays trying to keep the truth about Zak's nature secret, the other Secret Scientists found out and began pursuing Zak, forcing the Saturdays to go on the run. It is not yet revealed if Zak's true destiny is to be the destructor of humanity. It is said by Rani Nagi that, Zak is "All Kur".
It is possible that the Naga relic or Rani Nagi herself is the main reason why Kur was evil thousands of years ago as Rani Nagi could have directly taken control of the ancient Kur because in the Enûma Eliš, the Babylonian creation myth, Kur was depicted as a serpent-like dragon (Like on Zak's shirt).
Another is simply that the original Kur's power incarnated into the nearest sufficient host when its stone was disturbed.
- Kur is not located in its tomb, even though the Kur Stone said it would be. It is notable, however, that the stone may have been deciphered incorrectly. But later it is said Kur would be revealed in Antarctica, not necessarily found.
- At the beginning of Kur Rising a symbol that appears to be the letter c with a line connecting to a circle is shown on the Kur Stone. The same symbol appears at the end but this time appearing in Zak's eye. Jay has revealed that that symbol means Kur: http://forums.toonzone.net/showthread.php?p=3404647#post3404647.
- Several episodes showed a vision of Zak having embraced his Kur powers and controlling a cryptid army to overthrow humanity.
- Technically Kur is the only Saturday cryptid that appears in every single day of the Saturday's life because Zak has lived 13 years, so Kur has been there 13 years.
- Drew was indeed pregnant with Zak when the Kur stone was discovered. When the stone released a type of energy, which was really Kur's essence, it made its way into Drew's womb where it was infused with the unborn baby which Kur was reborn into. This means that technically, Drew gave birth to a cryptid.
- The episode Kur hinted that the Kur power was sentient and was responsible for causing a surge in Zak's powers, even influencing his mind to disrupt the Saturday's plans to stop the Nagas, almost in an attempt to assist them in overthrowing the human race.
- In War of the Cryptids, Zak/Kur was officially dead for three minutes. Zak S. is living and okay.
- In Hungarian "Kur" (kör) means circle which is the sign of limitless and endless.
- Kur also means Ancient large, or inferior hound.
- Because Kur was known as an evil, destructive creature, it can be presumed that his antimatter counterpart, the Anti-Kur, was a benevolent being.