The Unknown Thief, also known as Mr. U.R. Gonnadie, was a mysterious kidnapper of the Protopet. the Unknown Thief was later revealed to be Angela Cross.
Ratchet & Clank: Going Commando
The Thief kidnapped the Protopet and later Clank. The Thief attempted to scare Ratchet but only angered him, e.g., by electrocuting Clank.
After being defeated by Ratchet the Thief fled but later confronted Ratchet again and was revealed to be Angela Cross, a female Lombax.