At some point, a massive Ramlak attacked his home and consumed all the water leaving the land desolate. The act filled Koinelius with rage and he became fixated on getting revenge on the beast for the destruction of his homeland. This event also saw the loss of Tunar's leg to the creature which he replaced with a metallic piece. Thus, he took command of a ship and assembled a crew of Fishmen with the task of hunting the creature down. Though he claimed his actions were in the best interest of the crew, Captain Tunar cared little for them and only the death of the beast mattered to him. As such, he felt that those that were not single-minded in the pursuit of his mission were weak and needed to be discarded. This was because he felt that those who failed in the mission could always be replaced with a new crew.
His journey through the Sand Sea led to traps being placed with food along with nets being used to entrap the Ramlak. On one such occasion, his crew accidentlly captured the ThunderCats under the leadership of Lion-O who sought vengeance against Mumm-Ra for the death of his father Claudus. After their capture, Captain Tunar laughed at Lion-O's commands to let them go and declared that his crew would flay them as well as eat the ThunderCats. They were saved by the sudden attack of the Ramlak which Captain Tunar attacked with the assistance of the freed Lion-O. Seeing his courage, Kornelius believed that he was better than his own Fishmen crew who he deemed were cowards. As such, he decided to spare Lion-O and made the ThunderCats part of his crew as they sought out the Ramlak.
During their time together, Captain Tunar revealed his past to Lion-O who decided to help in his hunting down the beast. Their journey led the pair commanding the ship into a storm and into a confrontation with the Ramlak which split their vessel in half. Seeing the crew drowning, Lion-O decided to save them after seeing how single-minded Tunar was on revenge to which Koinelius called him "soft". As Lion-O saved the crew, Cornelius launched a harpoon at the beast and was thrown into the Sand Sea where he was seemingly killed. Following the death of the Ramlak, the Fishmen settled into the new oasis formed by the water and told Lion-O not to feel sorry for Captain Tunar as his fixation on revenge was his ultimate downfall. The lesson of Koinelius Tunar taught Lion-O the dangers of seeking vengeance and he ultimately decided to turn back in order to seek out the Book of Omens.
Koinelius' personality seems to be similar to that of Captain Ahab's from Moby Dick, as he so obsessed with the Ramlak, that he doesn't care what happens to his ship of crew and dies at the Ramlak's hands.
- When he finally harpoons the Ramlak, he yells "For hates sake, I spit my last breath at thee" which is a famous final quote Captain Ahab from Moby Dick yells at his enemy Moby Dick.