Focusing on the profession:
* Tragedians: This refers to performers who specialize in serious, often somber, drama.
* Serious actor: This emphasizes the opposite of a comedic performer.
* Non-comedian: A general term for someone who does not perform comedy.
Focusing on the personality:
* Serious: This describes someone who lacks humor or lightheartedness.
* Dour: This emphasizes a gloomy or sullen personality.
* Humorless: This explicitly indicates a lack of sense of humor.
Focusing on the effect:
* Serious: This refers to someone who creates a somber or solemn atmosphere.
* Dull: This describes something boring or lacking in entertainment value.
* Unfunny: This directly contradicts the comedic effect.
The best opposite word depends on the specific context and what you want to emphasize.