The term comes from fanspeak, the slang of science fiction fans, and originally referred to prolific writers of letters to fanzines and professional science fiction magazines of the early twentieth century. It was considered to be an important part of fanac ("fan activity").
Many letterhacks became well known throughout the industry. Writer Mark Engblom describes the phenomenon this way:
Chosen by the title's editor (or, in some cases, the writer), a few lucky fans would get the opportunity to share their opinion with not only the creators, but a captive audience of fellow fans as well. In fact, some of the most prolific fans had letters printed almost every month in a variety of titles, becoming minor celebrities in their own right.
The 1994 Squiddy Awards featured a "Favorite Letterhack" category. Some of the most prolific "LOCers" or "letterhacks" include: