Conversation so far:
How did Conan O'Brien start on Saturday Night Live?
In January 1988, Saturday Night Live's executive producer, Lorne Michaels, hired Conan O'Brien as a writer.
Did Conan O'Brien have any big skits on Saturday Night Live?
During his three years on Saturday Night Live (SNL), Conan O'Brien wrote such recurring sketches as Mr. Short-Term memory and The Girl Watchers.
Who did Conan O'Brien write the most for?
Conan O'Brien managed to craft what are regarded as some of The Simpsons' most memorable and finest episodes: Marge vs. the Monorail and Homer Goes to College.

Question: What did he do before this?
Self-contained rewrite: What did Conan O'Brien do before writing for The Simpsons?