The first version of Garry's Mod (Garry's Mod 1.0) released 20 years ago today (December 24 2004) by Garry Newman as a mod for Half-Life 2, which released just over a month prior. After several revisions, this became the more familiar Gmod 9 in the following year (2005). The image above is one of the first known images of gm_construct, made around this time. Credit to MaiaU for this screenshot.
(Edited)