Alvega was the planet closest to Skaro. It was the homeworld of the Amarylls and their Controller, which was situated at the core of Alvega. The planet was covered in rich vegetation and had almost no animal life save for giant earthworms.
After the Daleks finally achieved space flight, Alvega was the first planet the Daleks attempted to conquer. The Controller and the Amarylls fought back, resulting in most Daleks and Amarylls being lost.
The Dalek Fleet having moved on to other planets, only one Dalek remained, reaching the Controller and destroying it, causing Alvega to explode. The Dalek Emperor observed the explosion and decreed that whatever the Daleks could not conquer, they would destroy. (COMIC: The Amaryll Challenge)