handler

noun4

1. •
   One who handles something (especially manually) or someone.

   • The handler of a weapon gets a symbolic sensation of deadly power.
2. •
   A controller, trainer, someone who handles a specified thing, animal or person (especially a prizefighter).

   • The spy's handler told him to approach the subject by posing as a dog handler.
3. •
   An advisor or manager providing guidance to a person occupying public office or a prominent position.

   • The governor received guidance on how to best disseminate key information to the public from her handler.
4. •
   A subroutine that handles a particular situation such as an event or exception.

   • If the expression is a throw, we unwind the stack seeking a handler expression. — 2006