invoker

noun6

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