Simplify the following text for a Grade 7 native English-speaking person.
Original: The main characters are a friendly purple hippopotamus called Peter Potamus and his friend So-So the monkey .
Simplified: It featured Peter Potamus the hippopotamus ( voiced by Daws Butler impersonating Joe E. Brown ) and his sidekick , So-So the monkey ( voiced by Don Messick ) . Peter was big , purple , and friendly .