invoker

Short definition from Wiktionary

Noun

1. 1
   One who calls upon (a person, especially a god) for help, assistance or guidance.
2. 2
   One who appeals for validation to a (notably cited) authority.
3. 3
   One who conjures up spirits with incantations.
4. 4
   Someone who induces as an inevitable consequence.
5. 5
   One who solicits, petitions for, appeals to a favorable attitude.
6. 6
   That which causes a program or subroutine to execute.