For this reason modders would often collaborate on various fan sites, pooling resources and sharing documentation with one another. However, more complex modifications, such as changes to the gameplay mechanics or the addition of custom models and/or maps were not possible without more advanced tools specific to GTA, along with commercial-grade modelling programs such as SketchUp, 3ds Max and Zmodeler. In most of the games, certain data files were stored in simple archives or in plain text files, allowing modders to edit them using basic tools. One of the best-known examples is the iCEnhancer graphics modification mod by Hayssam Keilany, praised by reviewers and labelled as 'arguably one of the best mods of all time' by Polygon. In the following years the modding scene became more sophisticated and complex, as various aspects of the game's internals are gradually being discovered and documented by hackers. The use of a 3D game engine (the first in the series ) allowed development of custom vehicles, textures and character models, followed by new missions and map modifications the success of these new types of mods then started to attract widespread attention. While mods for Grand Theft Auto have been developed by hobbyists since the release of the first game, it wasn't until the release of the wildly successful Grand Theft Auto III on Microsoft Windows, in May 2002, that mods started to become both more accessible and more popular.

Mods for Grand Theft Auto are generally developed for use on the PC versions of the games, since the platform does not prevent modifications to installed software however, similar content for console and mobile phone versions does exist to an extent. Third-party software has been indispensable for building Grand Theft Auto mods, due to the lack of official editing tools from the developer, Rockstar Games. Frequently created by anonymous ' modders', modifications are presented in the form of downloadable files or archives. These unofficial modifications are made by altering gameplay logic and asset files within a user's game installation, and can drastically change the gameplay experience: from gameplay enhancements and alterations to its mechanics, to replacing the player's character model with a different character model or even something outlandish such as spawning zombies throughout the map. User modification, or modding of games in the open-world sandbox Grand Theft Auto series is a popular trend in the PC gaming community. While vehicles in the Grand Theft Auto series are loosely based on real-world makes and models, custom vehicle models such as this Audi R8 are a popular form of modification throughout the GTA community.

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