In honour of National Pet Day here is a look at six of the richest pets of all time. These cats and dogs have more money than most people. 6. Boo, the Pomeranian owned by Irene Ahn, is worth $8-million and has his own brand and book. The pup was worth $8 million. 5. Tommasino the cat was left a $13 million fortune upon the death of his Italian owner, Maria Assunta. He also owns castles, villas and estates. 4. Oprah Winfrey's five dogs are each to receive $30 million upon her death. 3. Olivia Benson, Taylor Swift's cat, has starred in ads for Coke and Keds Shoes. She's worth about $97 million. 2. Grumpy Cat, one of the most famous animals on the planet, is worth close to $100 million. 1. Gunther IV — heir of German Countess Karlotta Liebenstein's dog, Gunther III — is the richest animal in the world with $400 million.