initialer

noun3

1. •
   One who initials a document.

   • Initials affixed in this manner do not, therefore, by themselves bring the initialer into any connection with the order for criminal purposes. — 1947
2. •
   The artist who decorates the initial letters in an illuminated manuscript.

   • Often the ornamentor was an apprentice to the real artist of the scriptorium, the initialer. — 1946
3. •
   The initial episode of a television show or series of films.

   • Under Nicholas Ray's sock direction, the Marlon Brando mannerisms displayed in the initialer are gone and the role here carries much greater audience sympathy and response as a result. — 1991