The Gang of Four was an early fandom acronym for the four principal characters in classic Daria fanfiction who seem to travel together (in canon: "Road Worrier," "That Was Then, This Is Dumb," "Write Where It Hurts").
Typical GOF Configurations
This is the basic Season 1-Season 3 group used by many fanfic authors at the time (1997-1999). The Gang of Four included:
The four were romantically paired off as Daria/Trent and Jane/Jesse. The creation of the latter was probably influenced strongly by "Road Worrier," thanks to a scene in which Jane Lane and Jesse Moreno are shown leaning against each other, asleep in the back of the Tank. "Write Where It Hurts" also indicates a closer than expected relationship between Jesse and Jane. Quinn, in Daria's imagination, sees Trent and Jesse on horseback, and cries: "But look! Here approaches Mr. Lane himself, along with his sister's admirer, Mr. Moreno." This means Daria believed Jesse liked Jane (as in liked liked). The Jane/Jesse coupling takes a damaging hit in "That Was Then, This Is Dumb," when at the flea market it becomes clear that Jesse is not listening to anything Jane says.
This dynamic became less common in fanworks after series 3 (and after the show ended), as it became less common to see in the show itself and as fanfic writers started to become more interested in different characters.