Microsoft engineer Tony Krueger, who passed away recently, left an indelible mark on computing that billions use daily without knowing his name. While his Wikipedia entry credits him with porting Chip's Challenge to Windows, his deeper contribution to Microsoft Word fundamentally changed how we interact with text editors.

Krueger worked across multiple Word versions from 1.0 through 6.0 and beyond, likely holding the record for most Word releases shipped. Early spell checkers blocked users completely - you'd trigger them and wait while the program found errors one-by-one. Krueger's innovation made spell checking unobtrusive by running it during idle time and displaying red squiggles immediately under misspelled words.

This background spell check feature was so impactful that when Penn and Teller learned about it from a colleague, Penn announced to the entire theater: 'The red and green squiggles!? I love the red and green squiggles!' Teller silently concurred. Years later, 'Weird Al' Yankovic even featured the red squiggles in his 'Word Crimes' parody video.

Today, red and green squiggles appear in virtually every word processor and text field across operating systems. Krueger essentially reverse-engineered the MS-DOS spell checker to create this feature without original source code. The next time those squiggles catch your typos, remember Tony Krueger's quiet revolution in user experience design.