Vladimir Propp analyzed Russian folk tales and identified that they follow a common pattern of 31 narrative functions. Some of the main functions include trickery by a villain, a hero being tested by hardship, and a character being transfigured or deceived. Propp also found that tales typically involve 8 types of characters, such as a villain, helper, hero, and princess. His theory was that most stories adhere to a structure of these recurring functions and character types.