Tritonis is one of two major city states that make up the continent of Atlantis; the other being Poseidonis. Tritonis is named for the Greek god Triton, the son of Poseidon. In some sources, Triton has also been addressed as Tritonis. In contrast to the human-like Atlanteans of Poseidonis, the people of Tritonis are mostly Merpeople.
Untold millennia ago, groups of pilgrims settled in the greater Atlantean region establishing twelve distinctive communities, a few of which evolved into modern settlements, including Tritonis. Many believe that the original twelve settlements represented the twelve signs of the Zodiac.
In approximately 9,500 BC, the face of Atlantis changed forever. A massive earthquake ripped across the continent killing untold millions of people. However, many Atlantean scientists had prepared for such a catastrophe and constructed large force shields, which protected several major cities from the devastation, such as Poseidonis. Tritonis however, was left vulnerable and was all but destroyed. Nothing could prevent the entire continent of Atlantis from sinking permanently into the sea.
Following the Great Deluge, those Atlanteans who survived were sequestered inside the domed city of Poseidonis. The Atlantean mystic, Shalako felt that the technocratic Atlanteans were "unclean", so his followers and he mounted an exodus through the tunnels beneath the city and re-established themselves in Tritonis. Shalako used the dark magics at his command to create a hard-water dome around the city that protected the Shalakites from being crushed by the ocean depths. Shalako's brother, Orin, had developed a means to transform the Atlanteans into an amphibious race, and offered this technology to the Shalakites. Shalako refused Orin's offer, but his followers readily accepted the ability to leave the confines of their city at their choosing. Shalako took this as an insult and the ultimate betrayal. He cursed the people of Tritonis, transforming them into a scaly race of fish-people. 
Shalako's malign act was discovered and the Shalakites turned on him, killing him with their spears. They then set about to slaughter as many of his family members as they could find, including his surviving wives. Shalako's son, Dardanus, survived the massacre however and remained hidden for many years. Following the death of Shalako, the monarchy of Tritonis was passed to the venerable, but wise, King Stearn. 
Over the span of centuries, Tritonis survived as an isolationist settlement beneath the seas. Those who survived the cataclysm adapted to their new marine environment. The dominant race in Tritonis were the Mer-people, men and women with the upper body of a humanoid and the lower tail of a fish. While their neighbors in Poseidonis expanded their technological capabilities, the Tritonians preferred concentrating their knowledge in the realms of magic.
Several years ago, Tritonis was ruled by the merman known as King Firft. Firft was a glory seeker who held fast to the old traditions. Inwardly though, he always envied the riches of Poseidonis. His niece, S'Ona, was married to Iqula - the finest warrior in all of Tritonis. S'Ona knew that her uncle was unfit to rule and initiated schemes to put her husband on the throne of Tritonis.
At this time, Tritonis was the target of the Ocean Master who attacked all of the major Atlantean cities in an effort to acquire the twelve Zodiac Crystals that would give him supreme power. Ocean Master's scheme was foiled by his brother Aquaman. 
Tritonis was devastated in the Crisis on Infinite Earths, but was rebuilt not long after.
A short time later, King Firft learned that Poseidonis had been attacked by the sovereign nation of Oumland. He sent his finest warriors, led by Iqula to Poseidonis to impose a forced protection of the city. This action met with resistance from Aquaman who defeated Iqula in one-on-one combat.
Firft was ousted when he and several warriors cast their lot with Black Manta and attacked the surface world. Iqula sided with Aquaman in defending Poseidonis and the surface world and even arrested several of his former comrades. 
With Firft gone, Iqula became the new king of Tritonis. He maintained the city's isolationist traditions and had little to do with Poseidonis after the Black Manta affair. A short time later, Poseidon suffered great turmoil once again as the entire city began to slowly rise to the surface. Hundreds of displaced Poseidonians were forced to seek refuge in Tritonis. King Iqula reluctantly allowed them to enter the city, even though it went against all of their most rigid beliefs. When the situation worsened, Iqula had the Poseidonians pressed into servitude. Ultimately, it was the young mage Tempest who convinced Iqula to let the Poseidonians return to their home city. 
- Tritonis is named for the Olympian god of the tides, Triton, the son of Poseidon, Lord of all the sea.
- Tritonis is also the name of a salt water lake in Libya, North Africa. According to legend, this was also the home of the Haliad sea nymph, also named Tritonis.