Midgard Serpent

The Midgard Serpent is a machine designed to destroy life on Eath. It is the main threat in the game Tomb Raider: Underworld,

In Norse Mythology
Jörmungandr ( Old Norse Jǫrmungandr, pronounced [ˈjɔrmuŋɡandr]), often written Jormungand, or Jörmungand and also known as the Midgard Serpent (Old Norse: Midgarðsormr), or World Serpent, is a sea serpent, the middle child of the giantess Angrboða and the god Loki.

According to the Prose Edda, Odin took Loki's three children by Angrboða, the wolf Fenrir, Hel and Jörmungandr, and tossed Jörmungandr into the great ocean that encircles Midgard. The serpent grew so large that he was able to surround the earth and grasp his own tail. As a result, he received the name of the Midgard Serpent or World Serpent. When he lets go, the world will end. Jörmungandr's arch-enemy is the god Thor.

Tomb Raider Underworld
In Tomb Raider: Underworld, the Midgard Serpent is revealed to be a Doomsday device hinted to be Atlantean in origin instead of actual serpentine beast. Its activation can bring about Ragnarök, the Norse end of the world. The generally accepted role for the Mechanism is that it is some sort of deterrent Doomsday device. It was placed right on the spot where Pangaea, the primordial earth plate, first cracked apart. As such, Lara's effort to stop both device and Natla basically plays Thor's role in his fight against Jörmungandr in myth.

Trivia

 * Lara speculates that Níðhöggr, a great serpent that gnaws at the roots of the World Tree Yggdrasil is another manifestation of Jörmungandr.
 * If one looked closely on the top of the Midgard Serpent as it activates with Natla lecturing its true nature, one can see a serpentine statue rising, confirming the device's serpent motif.
 * It is unknown if the machine is named after the real Midgard Serpent or if in the context of the game's universe if the serpent even existed.