The Vorlon Planetkiller is an incredibly large and powerful
capital ship, it dwarfs even the
Vorlon Mothership. Compared to other ships, its length appears to be over 20 km.
The Planetkiller is the ultimate display of the power of the Vorlon Empire, it has the capability of destroying an entire Earth-sized planet. It is unknown how this weapon works, since there has been no survivors to tell their tale.
The ship was brought into the observation of the younger races when the Vorlons stepped-up their aggression against the Shadows during the final Shadow War. The Vorlons moved to exterminate any race that had any contact, or Shadow Influence, by destroying the planet itself.
The Vorlon Planetkiller made its first appearance in the episode "The Summoning", where it was seen with miniscule looking Vorlon Cruisers and Vorlon Motherships.
The Vorlon Planetkiller was in orbit around Centauri Prime when the Vorlons recalled it to Coriana 6 where it was destroyed by several of the First Ones in "Into the Fire"