Sekrion

Sekrion, Nexus Mind was a Vex Axis Mind that controlled and oversaw the Vex's expansion through Venus' planetary crust. It takes the form of a large Hydra that uses its constant barrage of Void blasts to quickly eliminate enemies while simultaneously defending itself with its indestructible shield.

Nexus Mind
Sekrion's sole purpose is to make sure that the Vex expand throughout all of Venus. Sekrion uses its impressive computational capacity to coordinate the Minotaurs operating through it.

Events of The Dawning
Two years after Sekrion's defeat, the Vex restarted their expansion throughout Venus. They rebuilt and upgraded Sekrion with a new chassis and technology from the Vault of Glass. Meanwhile, the Taken, despite Oryx's defeat a year prior, organized an invasion and attempted to take the Nexus Mind. They were either successful in taking Sekrion, or were beaten to the Nexus Mind by a Fireteam of Guardians. Regardless, it was destroyed once again.