People who write or compose things in a series, like a series of books or a series of music pieces.
Serialists are usually very organized and like to work on things in order.
Examples:
The serialists wrote many books about the same characters.
The music serialists composed a series of songs for the concert.
The serialists work very hard to make sure everything is in the right order.
The serialists are like the bosses of the series.
The serialists wrote a whole bunch of books, one after the other, about the same people.
The music serialists made a whole bunch of songs that all go together in a row.