One of the Chronovores that existed within the Space Time Vortex. Kronos was brought to Earth by the ancient priests of Atlantis and entrapped within the Crystal of Kronos.

Driven mad by this, when the Master sought to dominate Kronos by using the crystal, Kronos escaped and destroyed Atlantis.

Shortly after the island sank, the Doctor and the Master found themselves trapped in the Space Time Vortex by Kronos, who wished to thank the Doctor for releasing it.

It also planned to punish the Master by making him a servitor for eternity, but the Doctor begged to take the Master and have him tried for his crimes back on Earth. Kronos agreed, but during the debate the Master made his escape. .