In the initial stages of the web, stylistic and display properties were left largely to the preferences of the user. As more computers came online, the need for pre-designed looks and layouts became obvious.
On Oct. 10th, 1994 Håkon Wium Lie introduced the first proposal for a cascading style sheet. Adoption was slow and rather bumpy, but today the CSS3 specification is highly advanced and fully supported by all major browsers.
Cheers to Mr. Lie for setting in motion the visual web we know today!
Read the original proposal:
Read an interview with Håkon: