The Kithrawl is a huge Tineback creature with devastating flaming AOE attacks that can be fought as the level 80 Worldboss on Ruhnuk.
Unlike other Worldbosses in SWTOR, the Kithrawl is unique in the fact that is was designed against “prog” meaning that you go in solo or with a few friends, kill it and leave, unlike other Worldbosses that can sometimes require large groups of coordinated players.

With a pool of 36 million HP, it can take some time to kill as a completely SOLO player with a healing companion however the boss itself doesn’t deal a lot of damage, meaning it can take around 8-10 minutes to kill which is roughly the same time as some raid bosses in SWTOR. The only brutal attack you have to be careful for is the red circles of fire that the Kithrawl places all over the floor.

While standing in a single red circle is completely healable by a Companion, your Companion themself may die if they stand inside of 2 overlapped circles. You can pretty easily remedy the situation each time the Kithrawl drops red circles by clicking the Passive button on your Companion then turning it off again after the fire drops. Both the Kithrawl’s Gore ability and the red cone attack from the Kithrawl’s tail should easily be recoverable by any companion of influence 25 or above.
That being said I highly suggest checking out the Worldboss arena each time you visit Ruhnuk for Dailies as you can easily help another friendly player with Shared-Mob tagging and get credit for the [WEEKLY] in doing so.

Killing the Kithrawl will also grant you a Codex Entry, which I have listed below. There is also an achievement for completing the [WEEKLY] to kill the Kithrawl 5 times.

One of the most legendary creatures ever encountered on Ruhnuk is also one of the strangest, most inexplicable Tineback aberrations ever documented. Called “Kithrawl”–and sometimes “The Flame in Darkness” by those who survived crossing its path–the enormous beast was discovered by some unfortunate members of the ill-fated Gatressa Mining Conglomerate operation. Eyewitness accounts describe the beast’s skin as charred, blackened stone striated with something that resembled magma-filled cracks. The survivors contend that the creature was born among molten veins in the depths of Ruhnuk’s crust, but many dismiss these claims as the ravings of traumatized disaster victims. These reports, however, were enough to tempt the ambitious and the greedy into seeking out Kithrawl for its many imagined treasures, like the hardened pads of its feet or the deadly spines on its tail. Foolish opportunists have been said to forfeit their lives in pursuit of these prizes, while others suggest that Kithrawl might possess some of the most valuable and delicious meat in the galaxy. Realistically, anyone insisting they have firsthand knowledge of the details of Kithrawl’s lair is most likely exaggerating, intent on regaling local cantina-goers with their tales in exchange for free drinks. Since no visual proof of Kithrawl has ever been presented, only the unsuccessful hunters know what truly waits in the darkness below Ruhnuk’s surface.

Kithrawl, the Flame in Darkness Codex Entry

You can also unlock a special, hidden bonus Codex Entry by clicking on the small golden Dagger that you can find ontop of the massive pile of bones in the far-back of the Kithrawl’s Worldboss Arena. You don’t need to kill the Kithrawl, you can just walk around it and click on the Dagger once you find it.

Born on an unremarkable planet in the Outer Rim, the boy who would become Master Dunesa Rul apprenticed with the local metalsmith to provide additional income for his family. Accounts of his early life learning the trade are few, but historians agree that Rul showed exceptional natural skill and quickly outgrew the simple routine of the frontier smithy who taught him. Seeking more significant challenges, Rul found work at several smithies across the Core Worlds. The quality of his weapons gained recognition among the Mandalorian clans, and with their patronage, he opened his own forge at a remarkably young age. Rul’s creations, prized within the Mandalorians, were often handed down from one clan leader to the next, but demand for new work was overwhelming. Rul was killed in an explosion during an altercation between Clan Mettir and Clan Ironstone, who sought to lay claim to a masterwork weapon–a durasteel dagger–he had created. Both clans were hunted down and destroyed in retaliation for the grievous loss. The dagger itself was never found.

Mandalorian Relics: The Final Blade of Dunesa Rul Codex Entry