Wilbur is the main antagonist of Bubble Witch 3 Saga until Level 501, where he is reformed to compete with Nero. It also comes with a level of him. His first level is Level 10 to defeat Wilbur. He kidnaps the Queen of the Fairies and keeps her prisoner, alongside owls and other fairies.
Stella and Nero imply during a talk that Wilbur once was a nice cat, but somewhere down the line was corrupted and became mean. Nero is teaching the cat to become nice.