The Kzinti are a feline-like species native to the planet Kzin. They are an aggressive, imperialist people that have fought numerous conflicts with almost all of their neighbors, including the Federation, the Klingons, and the Gorn.
(From Memory Alpha)
It is believed that the Kzinti had achieved spaceflight by the early 18th Century.
The Kzinti hads a history of conflict with Earth, as the two planets fought a series of four wars between them. In what was collectively known as the Earth-Kzin Wars, Kzin was always the aggressor and Earth was always the victor. The first was fought sometime after First Contact in 2063, and the last was concluded by the end of the 2060s.
Following the signing of the Treaty of Sirius, the Kzin government, including all Kzinti territories, were essentially demilitarized. The Kzinti were forbidden to possess any sort of weapons or starships – except police vessels, which were to be used solely for peacekeeping. In 2269, Dr. Keniclius 5 cited the Kzinti's ongoing rivalry with Earth as a reason for the necessity of eugenics experiments to improve the human breed. (The Animated Series: "The Infinite Vulcan")
Later that year, Kzinti archeaologists discovered two Slaver stasis boxes on Kzin. They turned one over to Starfleet to have transferred to Starbase 25; the second they kept for themselves, only to discover that it was empty.
Based on various lucrative finds in previously discovered stasis boxes, the Kzinti hoped to find a potentially powerful weapon, which they could use to defeat the Federation. Secretly supported by the Highest fo Kzin, some privateers acquired a "stolen" police vessel to conduct their mission. If they were successful in their theft of the other stasis box, they would be heroes; if they failed, they would be repudiated by the Kzin government.
On Stardate 4187.3, a group of Kzinti privateers lured the long-range shuttle Copernicus into the Beta Lyrae System, using the empty stasis box. They then captured the crewof the Copernicus on the surface of a barren ice planet, placing them in a police web aboard their privateer vessel, the Traitor's Claw.
Upon inspection of the stolen stasis box, the Kzinti discovered a Slaver weapon, whose functions they immediately began to test. By the time they reached the last function, the device, a sort of "smart computer", interpreted the Kzinti as enemies and self-destructed, killing three of the Kzinti privateers and severely damaging their vessel. (The Animated Series: "The Slaver Weapon")
For centuries, the Kzinti waited and watched the galaxy around them for the perfect moment to renew their war with the Federation and extract some measure of revenge for having to endure the percieved humiliation brought on by the Treaty of Sirius. Following the destruction of Romulus in 2387 and the renewed tensions between the Federation and parts of the Klingon Empire, the Kzinti struck in early 2388. Details of the war can be found HERE.
The Kzinti were large, carnivorous, cat-like beings that often stand over 8 feet tall and can weigh nearly 500ibs. Their anatomy was extremely well reinforced, as they possessed multiple hearts, and vertical braces along their ribs. They do not possess backward-bending legs, but walk much like other humanoids. Males usually have orange-brown fur; female coloring varies but black fur is rare. All have prominent fangs and large tufted ears. Each hand has three fingers and an opposable thumb, each with its own retractable sharp claw. They are powerful beings, and like other felines, are quick, agile, and possess remarkable balance.
Kzinti speak in a hissing language called The Heroes Tongue. In its written form, the language is full of commas, dashes, and periods.
Some male Kzinti were capable of reading minds; however, psychologically, they were often unhappy and neurotic. Although there were no sure ways to prevent a Kzinti telepath from reading someone's mind, it was found that mental imagery of eating vegetation dissuaded them from making such attempts.
The Kzinti are a prejudiced, war-like, and violent species who often spoke of pride and honor. Males had no respect for males of herbivorous species, such as Vulcans, or of females of any species. This lack of respect stemmed from the fact that on their homeworld, Kzinti females were simply "dumb animals". Males are also tempermental, arrogant, and prone to impetuous behavior.
There is no monetary system in their culture; instead, the Kzinti follow a rigid honor system.
If a Kzin was defeated in battle but allowed to live, that action was considered the ultimate insult. In such a case, the Kzin had to seek revenge by challenging the attacker to a duel before the attacked Kzin was allowed to seek either medical assistance or reinforcements. The Kzinti are not named at birth; they must earn their names through valorous deeds, typically ones that advance the interests of the Patriarchy. Unnamed Kzinti have lower status, and are referred to by the name of their profession, such as Pilot, Groomer, or Scientist. Single-named Kzinti have distinguished themselves in some manner. They often follow their awarded name with the name of their profession. Kzinti can accumulate multiple names if they continue to perform valorously.
The Kzinti are governed by the Patriachy, which is comprised of the alpha males (chu'kalth) from each of the ruling Moujul (clan or "pride" in Federation usage). No females are ever allowed to serve in the government, and have no say in its laws or politics.