15 to 20 years
A humanoid race from the Gamma Quadrant, the Jem'Hadar are the military arm of the Dominion and one of the most powerful military forces in the galaxy. They were genetically-engineered to serve as warriors for the Dominion and were feared by races in and around Dominion space as the brutal face of Dominion oppression. They were engineered to be loyal to the Founders, are directly supervised and led by the Vorta, and are kept in check by a programmed addiction to the drug ketracel-white.
The Jem'Hadar are bred and grown in hatcheries or birthing chambers and have been known to be placed in stasis chambers until their awakening. For humanoids, the Jem'Hadar have an incredibly fast metabolic rate, due to modifications made to their genetic structure.
A Jem'Hadar baby is born looking almost mammalian and is fully grown within three days of leaving it's birthing chamber, which allows for very fast replacement of casualties. When they are older, they begin to take on a more reptilian appearance.
Within a day of maturation, Jem'Hadar children already possess advanced language skills and cognitive reasoning. Adolescent Jem'Hadar require food for consumption, which is also due to their higher metabolic rates. When they become full adults, their programmed addiction for ketracel-white as their only means of consumption fully manifests. Without large quantities of "the white," Jem'Hadar circulatory systems start to deteriorate. Initial symptoms begin to affect the Jem'Hadar as chemical dependency withdrawals, most typically muscle spasms. Subsequently, they become violent, killing first their enemies, then their allies, then finally each other.
The entire Jem'Hadar species is comprised solely of males. This allows the Dominion to breed armies of soldiers who possess no emotional attachment to their parents or siblings to distract their loyalty.
In 2405, a Jem'Hadar hatch pod became infected with humanoid DNA, which was effectively discarded by being ejected into the vacuum of space. This pod was later discovered by the USS Admonitor in 2407. All of the infant Jem'Hadar were killed by exposure to the vacuum, except for one. This was Jek'Kralija, the first Jem'Hadar female: the creation of a female Jem'Hadar was due to the humanoid DNA, which fertilized the eggs in the hatch pod with a J-chromosome rather than an L-chromosome (the genetic code of Jem'Hadar has LJ chromosomal pairing as a male).
They are taller than an average Human and with a wider build. Their skin is a leathery grey arrangement of scales with many horn-like protrusions across and around their face and back. Their species was engineered for strength and durability, to perform as the ultimate soldier.
As a result of advanced genetic engineering and combat breeding, the Jem'Hadar have excellent vision, and are several times stronger than Humans. All Jem'Hadar have the natural ability to cloak themselves, which effectively hides them from both sensors and the naked eye. The Jem'Hadar has no other needs. With the exception of their addiction to ketracel-white, they do not require sleep or any additional form of sustenance or nutrition. Activities such as sleeping and eating are considered a weakness and a distraction from a constant state of combat readiness.
Jem'Hadar usually die young in battle. As such, it is rare for them to live past the age of 15 years . Only a few get to live up to the age of 20. Those who do are awarded the title of "Honored Elders." No Jem'Hadar has ever lived beyond 30 years old.
Although the Jem'Hadar worship the Founders like gods, the most of the Jem'Hadar have never actually seen a Founder. Some even doubt that they even exist. However, they have built their service to the changelings into a form of religion, to the extent that the Jem'Hadar ritualistically commit suicide if they fail to protect a changeling from harm.
Jem'Hadar combat units follow a very specific hierarchy. Normally, a Vorta commands one or several Jem'Hadar units, usually consisting of 6-10 warriors per unit, each ranked by number. Every unit contains a Jem'Hadar First, who is in command. Each Jem'Hadar after the First is also given a number rank (Second, Third, Fourth, etc.). In the event the First is killed, the Second shall take over for the First, the Third will take over Second, and so forth. Although the succeeding Jem'Hadar will take over the duties of his superior, he will only receive the higher number rank if his Vorta commander allows it.