From Lazarus wiki
Mattias has provided more code for Lazarus project than anyone else, to all areas except maybe some widgetsets. He is the main expert in these areas:
- Codetools which are used by the IDE to parse pascal sources.
- Project related code
- Package related code
- XML libraries
- Many LCL classes and functions
- Many IDE features
... and so on. Search for "Mattias Gärtner" in Lazarus sources.