Zuzu's owner

An individual lived in the Edifice. He was tall, thin and humanoid, with pewter-coloured skin. He wore fluorescent coloured clothing which seemed oddly tailored to Donna Noble.

Zuzu's owner lived on Floor 165 of the Edifice, apparently by choice. He took his pet Zuzu for a walk everyday, going down several floors. He encountered the Tenth Doctor and his companion Donna on one of these walks. (AUDIO: The Forever Trap)