Magor is an unlikely myth that appeared around 2010 and 2011 in the Polish GTA community. It is a glitched version of Big Smoke that allegedly spawns because of leftover beta-era code.
Magor was first created on the now defunct GTA forum Grove Street Polska, where a user going by the name EmilMaserak442 created a post called "Dziwny bug", in which he detailed that Magor appeared after he finished the Pilot School once again to get the Gold medal, standing still in one of the hangars. He was able to go through him, as he had no blockmap and just stood in a T-Pose.
The name "Magor" was coined after the jumbled code that appeared in the right screen corner when Magor was approached, as it allegedly said "missing script/mago/R.wav". Some other of the missing text informations that allegedly appears when Magor is approached include "missing script/mago/chocolate.dll", "missing script/mago/owoce.wav", and "missing script/mago/bs_100prec.wav". Trying to find these files in GTA San Andreas, at least according to Emil, makes them "disappear" and makes it impossible to see Magor, which might prove the myth's falseness, but on the other hand, it is common for bugged/missing files to disappear upon trying to open them in early 2000's games (one example of this happening is in the first Far Cry game).
Many people claimed to be unable to see Magor, but it was soon researched that 100% completion is required, because it activates the missing leftover script, however, the script got removed in the Steam version and in several PC versions. It is most likely that only the rare pre-Hot Coffee version of the game has Magor script in it.
The myth resurfaced in 2018 on one of Polish GTA Discord chats, as the user Najman100PRO claimed to see Magor.