Popeye's Chimp

$$f(n) = \begin{cases} n/2, & \text{if }n\text{ is even} \\ 3n+1, & \text{if }n\text{ is odd} \end{cases}$$

Popeye's chimp is the first of the 7 evil deities that KFC monkey encounters. He is one of the biggest enemies KFC monkey has encountered and by far the evilest.