Zircon (species)

The Zirconians were a warlike species.

They created a galactic cyclone and directed it to Earth. The toxic gases in the cyclone would have destroyed most life on Earth, allowing the Zirconians to invade with minimal opposition.

In one account, they were stopped by the Third Doctor and Sarah Jane Smith, who warned Alistair Gordon Lethbridge-Stewart about the cloud. In another, the Fourth Doctor and Joan Brown were the ones to stop their plans, having warned Maxwell-Lennon. (COMIC: Doomcloud)