Tyranid
In the table-top wargame Warhammer 40,000, Tyranids are a swarm of aliens in many sizes and shapes. The most well known type of Tyranid is the horrific Genestealer. At first genestealers were independent monsters/race used in WH40K fiction and most importantly in table-top game Space Hulk. Soon the concept grew to a whole Tyranid race, of which genestealers are only one part.
Tyranids form a superorganism: they travel the universe on their Hive Fleets, destroying all ecologies in their path. They are psychically linked via their Hive Mind, which gives them great abilities to strategize and coordinate. When one Tyranid sees something, within an instant the entire Tyranid race is aware of it.
The mentality behind the Tyranid race can be summed up by the phrase "quantity has a quality all its own". From the lowliest Ripper swarm, to the deadliest Hive Tyrant, the signature trademark of Tyranids is that they swarm over their foes, obliterating everything before them without regard for species or race, seeing all life as merely fresh meat; new gene code to be assimilated, processed, and cycled into the spawning cycle to generate deadlier species off-shoots.
Tyranid Battle Tactics
Tyranid tactics are based around the notion of superior numbers. Tyranids overrun opposition in close combat, closing faster than most armies. They possess few ranged weapons, but their sheer numbers and close combat specialisation makes up for this if they are commanded by a worthy commander.
Tyranid Storyline
In Warhammer 40,000, the Tyranids appeared from the eastern part of the Galaxy, and sent a large fleet of troops (called Hive Fleet Behemoth) directly at the center of the galaxy. They were defeated, barely, by the efforts of the Ultramarines chapter of Space Marines, although the Ultramarines suffered devastating losses.
Later the Tyranids returned with Hive Fleet Kraken which, instead of throwing one mass of troops against the Imperium, split into countless smaller fleets, each small fleet enveloping whole systems before reinforcements could arrive. At the same time, Hive Fleet Leviathan appeared from "below" the Galaxy (in a 3D sense, on the Z axis) and attacked from two points, cutting off large portions of the galaxy from reinforcements.
