"Maybe it's like an ant hive... You know what I mean. There's, like, one female that runs the whole show... Yeah, the momma. She's badass man, I mean BIG."
- – Pvt. Hudson, Aliens
The Norn Queen (also known as Splicer-Beasts, or Tyrannicus Primagenitor) are the head honchos and matriarchs of an entire Tyranid Hive Fleet. These alpha bitches are in charge of the literal creation of entire Tyranid bioforms, from the smallest microbial phage-cells to the largest Hive Ship. They are the genetic architects of the Nids and THE MOST important and productive organism of the Nids. You know how the Nids usually scatter if a strong synapse creature dies? Now imagine if that one was in charge of an entire Hive Fleet. If she dies, the Hive Fleet would be unable to craft new creatures until another one is created, crippling the leadership and creature creation for a few short but crucial moments.
Norn Queens live upon massive Hive Ships in huge chambers at the center of the Hive Fleet and ingest genetic material, churning out the countless types of creatures that make up the Tyranid Hive Fleet. All Tyranids have links back to a Norn Queen, as the only way for Tyranids to reproduce is via this cloning technique. It is said that they lead the Tyranid forces and direct the evolution of the Tyranid race.
Norn Queens require a constant supply of fuel, in the shape of genetic material, in order to reproduce or bring forth new Tyranid life forms. This mainly consists of the fluids formed in Reclamation Pools, that are pumped up into the Hive Ships through massive Capillary Towers. Genetic material is also supplied directly to the Norn Queen via living creatures and scavengers, such as Coffin-Crawlers. All of this, including the transport creatures carrying the food, is pumped into the great jaws that are located at the top of the Norn Queen, and synthesized by the Queen's genetic shredder organs. The dissembled DNA structures form a gene-bank, which provides the raw material from which new creatures are created. Once a type of bio-construct has been designed, more identical creatures can be cloned by the Norn Queens.
Norn Queens are capable of bringing forth new bio-constructs in a variety of different ways, each designed to ensure maximum efficiency. Most bio-constructs are born as tiny wriggling larvae or may begin life as eggs that must be nurtured further before they hatch and develop into adults. Clusters of eggs spill from rows of ovipository orifices along its flanks, fluid filled depressions on its upper surface writhe with maggot-like larvae, fetal sacs hang like ripe fruit from umbilical branches, and huge larval Teleporter Worms burst from incubator pouches on the Norn Queen's sides. Simpler bio-constructs may emerge already in their adult form to be gathered and directed by the horde of creatures that feed and serve the Norn Queen.
As there is never any "mating" happening at any point in the Tyranid reproduction cycle, this means that Tyranids are an all genderless race of clones asexually reproduced from their Norn Queens.
Contrary to popular belief, Norn Queens don't always stay on their lazy ass up in space all the time. Sometimes, they hop on land and ride around in a Dominatrix. However, doing so is obviously incredibly risky, but it does lead to boosting the synapse leadership and coordination on the planet a thousandfold.
Most recently, with the advent of the 4th Tyrannic War and the return of Hive Fleet Leviathan, there's been sights of a pair of new creatures that are directly connected to the Norn Queen. These are the Norn Emissary and Norn Assimilator, and appear in battlefields with a specific objective and mission in mind, which is assigned by the Norn Queen into their minds so they can go and make sure it is accomplished.