The Lemurs migrated from alt.fan.lemurs to 000SUPERGUY, where they became a longstanding Superguy running gag. They lurked around the edges of the Superguy world, causing trouble at various pivotal points, such as stealing Spectrum's armor at the climax of the Industrial Revolution. (See Team M.E.C.H.A.) After that group's drop in activity, they migrated again to Earth-20 where they became one of the obligatory animal species infesting that world's LNHQ.
These lemurs are distinctly prone to mischief, and make "frink" and "ptang" noises wherever they are found.
Other, more human-hostile species of lemur have evolved in the LNHQ's subbasements. These include the giant, fanged deathlemur and the ghostly wraithlemur. With the LNHQ in space, they have begun marauding around Netropolis.
There's also the (perhaps related) Werewolf Lemur Incident of 2014, which the LNH doesn't talk about.
According to Superguy writer Gadge, who introduced the Lemurs, they were a BBS in-joke originated by Joel Furr, brother of fellow Superguy writer Rob Furr. Someone tried to insult him by calling him a "lamer" but typoed it "lemur" instead, and the rest is history.
- Whether the Lemurs have any connection to the Para.net.elemental Plane of Typo is under investigation.