Biology
Due to the brutality of their surroundings, natural selection has played a significant role in the evolution of the Cronin. Unlike most sentient species, Cronin eyes are wide-set - on Earth, this is common among prey animals, and in this case it gives the Cronin 240-degree vision, giving them greater visual acuity and awareness of approaching predators. Cronin eyes have narrow pupils. Their irises may be red, green, amber, or blue in color.
Their large shoulder humps store fluids and nutrients, enabling them to survive extended periods without food or water. A bigger shoulder hump is seen as a sign of high status, showing how successful an individual Cronin is at hunting. Their thick hides are virtually impervious to cuts, scrapes or contusions, and they are highly resistant to environmental hazards, including toxins, radiation, and extreme heat and cold. Consequently their diets can include food and drink which would prove very dangerous to other species—a fact reflected in the Cronin liquor of choice, ryknar, which is said to "hit aliens like ground glass". Younger Cronin have yellow or green markings on their hides. These markings darken to brown or tan over time, showing their age.
Cronin typically stand over 7 feet. Heavy creatures, Cronin have been known to weigh at least 150 kilos, upwards of nearly 200 kilos for above-average specimens, and counting guesses by non-Cronin observers even estimates of 800 pounds are made.
The most amazing physiological feature of Cronin biology is the multiple instances of major organs. These secondary (and where applicable, tertiary) systems are capable of serving as back-ups in the event of damage to the primary biological structures. They have, for example, two hearts, four lungs, and four testicles. This reflects in their slang, where they often speak about a "quad" where a human would use the words "balls" or "pair". Cronin also have a secondary nervous system using a neuroconductive fluid, meaning they are almost impossible to paralyze. Cronin bleed a yellow or orange fluid when shot, which may be this fluid or actual blood.
Aside from redundant systems, the legendary Cronin "blood rage" adds to the race's reputation for being notoriously difficult to kill or incapacitate in normal combat scenarios. In this state, Cronin become totally unresponsive to pain and will fight to the death regardless of injury level, with the side effect of reducing their capacity for logic and self-control.
Sheer physical hardiness means an individual Cronin can expect to live for centuries. Cronin can live for well over a thousand years, as evidenced by Warlord Okeer, a veteran of the Cronin Rebellions who died (of decidedly unnatural causes) well over a thousand years after the Rebellions ended.
Despite their natural propensity for toughness, Cronin do have physical weaknesses. According to a few people knowledgeable about them, if one lodges a knife at a certain spot near the frontal plate on a Cronin's head, the plate can be ripped off. It is apparently the one thing Cronin do fear.
History
For thousands of years, the Cronins have existed as a thrall race to the Solementi. Seen as the epitome of brute strength and dedication to war, the Cronins were encouraged to take their innate tendency to select the strongest and develop it further for the purpose of breeding only the best. The Solementi’s took these fierce warriors and populated several of their frontier planets with them, thus insulating themselves from outsiders with a race that felt an allegiance to them that was a great deterrent to invading Solementi space. Over the centuries this wall of Cronins has done exactly that to a degree that has made the Solementi all but a myth to outsiders. The Cronins on the other hand are all too well known and feared by those near to their space. Colonization on any of their worlds is highly inadvisable, at pain of death. Fortunately, the Cronins are as happy fighting amongst themselves as they are with outsiders and they believe that their sole purpose is to defend the Solementi Empire. Should they ever be released by the Solementi, the whole quadrant might easily fall to the Cronins.
Culture
The Cronin have a two-fold status. First and foremost is their adherence to a code in which they vow to the protection of the Solementi. It is almost a god worship, but it isn’t in that they simply believe that it is the correct way to live. Doing otherwise would be an apostasy and any that refuse to live by the code are cast out.
Internally, among their own kind, they have a strict superiority code based on the size of their humps. They frequently challenge one another to ritual combat for the purpose of proving their worth and advance their status. One does not challenge another if they are not of comparative size. It simply isn’t done. To challenge another Cronin above your own status, is to deny the natural order. The offending Cronin is put to death by his peers, without recourse to any sort of trial.
Men are the hunter gatherers - women the farmers, child rearers, and defenders of the home. It is nothing for male Cronin to be away from their home for extended periods of Campaigning. Campaigning is ritualized warfare for the purpose of training a more combat ready force.
In short, Cronin are one of the most adversarial races that anyone might encounter. The Alpha Quadrant has the Klingons and the Breen, while the Delta Quadrant has the Borg, the Hirogen, and the Cronin.