The Eminence

The Eminence was a gaseous entity that travelled across the universe in teleportation caskets. The Eminence could control the minds of any being it came into contact with, as long as it inhaled the breath of forever, turning them into its infinite warriors. (AUDIO: The Seeds of War)

Biography
The Doctor fought the Eminence "several lifetimes" before his sixth incarnation.

The Sixth Doctor once stopped the Eminence from infecting Earth's seed banks, thus rendering the Earth's colonies barren. (AUDIO: The Seeds of War)