handler

Short definition from Wiktionary

Noun

1. 1
   One who handles something (especially manually) or someone.
2. 2
   A controller, trainer, someone who handles a specified thing, animal or person (especially a prizefighter).
3. 3
   An advisor or manager providing guidance to a person occupying public office or a prominent position.
4. 4
   A subroutine that handles a particular situation such as an event or exception.

Proper noun

1. 1
   A surname.