Barney The Dinosaur Theory

1) Start with the given: CUTE PURPLE DINOSAUR

2) Change all U's to V's (which is proper Latin anyway): CVTE PVRPLE DINOSAVR

3) Extract all Roman Numerals: C V V L D I V

4) Convert into Arabic values: 100 5 5 50 500 1 5

5) Add all the numbers: 666

Thus, Barney is Satan.