Fivers are dedicated fans of the science fiction television show Babylon 5. As the B5 fan-base grew in the 1990's, some fans decided to venture into the versus-debating world to pit their favorite against the forces of Star Trek and Star Wars. Fan assessments of B5 capabilities vary widely from the extremely conservative estimates of BabTech-on-the-Net (no longer available) to the extremely generous estimates of the B5 Technical Manual.
Particularly rabid Fivers directed so much hatred toward BabTech-on-the-Net creator Brian Young that he took his site offline for a period of time.
At some point in the past, Fivers were also known as "lurkers".