Kyle R. Hofmann is a modder. He was 14 years old when Quake was released.
Hofmann released all his modifications as unified .DIF files, which had the benefit over .QC of displaying what was changed in each file. The downside of this type of file is that the user would need to copy and paste each piece of text over to the proper location in each .QC file, meaning it is less intuitive for the average user.
Note that many of the modifications made by this author are relatively simple in nature, often being little more than a slight tweak, which were quickly constructed and released. This latter fact resulted in many of Hofmann's modifications not working properly, either due to missing some feature or having flawed syntax.