* Mechanic: A person who repairs machines.
* Critic: A person who judges the merits of something.
* Technician: A person skilled in a particular technical field.
* Logician: A person skilled in logic.
* Linguistic: A person who studies language.
* Musician: A person who plays music.
* Politician: A person involved in politics.
* Academic: A person who works in academia.
* Electric: (not technically an agent, but refers to a person or thing using electricity)
* Mechanic: (see above)
Note: Some words ending in "-ic" are not noun agents. For example, "magic" is a noun, not a noun agent.