The Original Mythos are the original and earliest writings of the Slender Man Mythos. They include those written by Victor Surge and the SomethingAwful Paranormal Thread between June 2009 and February 2010. Some include early writings and creepypasta by other sources around the same time as part of the original mythos, although no slenderblogs or video ARGs are considered part of the original mythos, even though MarbleHornets was first created within the community and timespan.
The original mythos contain many differences, some very major, in Slender Man from the contemporary mythos. While not consistent in themselves, as they were a period of rapid evolution, change, adaptation, and creation of the mythos and traits of Slender Man, there were certain commonly accepted or prevalent traits that either differ or do not exist in the current Slender Man.
The original mythos are the focal point of the Surgist trend of Slender Man canon.
| Original Mythos | Contemporary Mythos |
| Slender Man has a face, which is visible except on film. | Slender Man is completely faceless, even in person to individuals. |
| Slender Man may occasionally wear hats or headwear. | Slender Man does not wear any hats or headwear. |
| Slender Man has cults or religious followings. | Slender Man has no cults. (Ex. DarkHarvest00) |
| Slender Man gains trust of victims. | Slender Man takes control of victims. |
| Slender Man has tentacles, sometimes they are used as legs. | Slender Man has no tentacles (Ex. TT, where it also uses them for locomotion.) |
| Slender Man can impersonate humans. | Slender Man cannot or does not impersonate humans. |
| Slender Man does not cause visual or audio distortion of media. | Slender Man causes visual or audio distortion on media. (Ex. MarbleHornets) |
| Slender Man consciously removes evidence, via fire. | Slender Man does not consciously remove evidence (Ex. EMH, TT). No link to fire. (Ex. MH) |
| Slender Man mutilates victims, including animals. | Slender Man does not mutilate victims (Ex. EMH). |
| Slender Man will aggressively attack its victims. | Slender Man will not aggressively attack its victims. |
| Slender Man's appearance means certain death. | Slender Man is not essentially dangerous, although his appearance is not a good thing. |
| Slender Man is under active watch by the government. | Slender Man is apparently not a being of interest or the government is not aware of it. |
| Slender Man is less concerned with remaining hidden/messy. | Slender Man leaves very little evidence of its existence. |
| Slender Man has no connections with other legendary beings. | Slender Man has connections with the Rake. |
| Slender Man rarely uses mind control. | Slender Man often uses Proxies. |
| Slender Man frequents the forest. | Slender Man has no preferred habitat. |
| Slender Man's prey is almost exclusively children. | Slender Man's prey is either undefined or mostly college students. |
| Slender Man often changes physical height or dimensions. | Slender Man is often extremely tall, but his volume dimensions stay the same. |