A letterer is a member of a team of comic book creators or an individual creator responsible for drawing the comic book's text.
The letterer's use of typefaces, calligraphy, letter size, and layout all contribute to the impact of the comic. The letterer crafts the comic's "display lettering": the story title lettering and other special captions and credits that usually appear on a story's page. The letterer also writes the letters in the word balloons and draws in sound effects. - Wikipedia