I am a mathematican. Since math is written in TeX, I have come to enjoy tinkering with the language; at the moment, I have one package on CTAN, ytableau, for drawing Young tableaux and Young diagrams in a variety of ways, some of which are not possible with the other such packages.
I am mostly proficient in the programming aspects of TeX and LaTeX, particularly the
pgfkeys package, which is a complete programming language in itself (and with much better syntax than TeX). All my good answers are either about macros or TikZ :)
My first "real" gold medal, finally, for my most popular question: LaTeX3 versus pure Lua!