Anders Hejlsberg

Sticking with the one person working alone assumption, I nominate Anders Hejlsberg. He wrote a Pascal compiler best known as the compiler component of Turbo Pascal. He wrote the compiler in assembly language for both of the dominant PC operating systems of the day (DOS and CPM). It was designed to compile, link and run a program in seconds rather than minutes.

Borland International bought the compiler and hired Anders. They bundled the compiler with a complete IDE (integrated development environment) and sold the complete development system for much less than other compilers on the market. The impact on programmer productivity was game changing.

At the time I was so impressed that I wrote "Using Turbo Pascal". The first of five editions was published by Osborne-McGraw Hill in 1986. Used copies still trade on sites like Amazon and Ebay.

Anders Hejlsberg went on to lead the team that developed Borland Delphi, a derivative of Object Pascal with the blazing speed of Turbo Pascal. Delphi is still widely used, ranking #13 on the TIOBE index. Anders then moved to Microsoft where he oversaw the development of C#. Currently ranked at #5 on TIOBE, C# is a valued workhorse in the world of Microsoft development.