invoker

1. One who calls upon (a person, especially a god) for help, assistance or guidance.

   An invoker of God's mercy

2. One who appeals for validation to a (notably cited) authority.

3. One who conjures up spirits with incantations.

4. Someone who induces as an inevitable consequence.

5. One who solicits, petitions for, appeals to a favorable attitude.

6. That which causes a program or subroutine to execute.

regular