Based on the profession:
* Tragic actor/actress: This refers to someone who specializes in dramatic, serious roles.
* Serious performer: A more general term for someone who performs in a non-humorous manner.
Based on the personality:
* Serious person: This describes someone who is not prone to humor or lightheartedness.
* Humorless person: This indicates someone who lacks a sense of humor or finds it difficult to appreciate.
* Dour: This describes someone who is gloomy and stern.
Other considerations:
* Critic: A person who analyzes and judges, often in a negative way, which contrasts with the entertaining nature of a comedian.
* Straight man: In comedy duos, the straight man provides a foil to the comedian's jokes.
Ultimately, the best antonym for "comedian" will depend on the specific context and meaning you want to convey.