Anyway, it depends on how bad-ass you want to be. If you want to go all out, go get a book on game "AI." I put AI in quotes because I am an AI snob, and don't consider game AI to be anything more than glorified state machines and if-blocks...but anyway...
If you just want to do a normal "AI" thing, you can assign properties to each monster (making each monster its own instantiated class is easiest). Then, per turn, tell it to update. The update can be as simple as checking distance relative to the character against some threshhold set as a property. This is the state machine method, and is pretty expandable.
