The Macintosh was the first computer most people had seen that used a mouse. Before the Mac, home users had little ability to create art or graphics with computers. Special drawing tablets were generally required. Computers before the Mac had very low resolution screens.

When Steve Jobs introduced the Mac to Apple shareholders in January 1984 and they saw Macpaint drawings flash across the screen (along with more than a few other groundbreaking features), they cheered. Bill Atkinson's Macpaint turned any computer into an art studio. Perhaps more importantly, anyone who did not consider themselves a serious artist could make cool graphics on a computer.

A New York Times review from 1984 called Macpaint "better than anything else of its kind offered on personal computers by a factor of 10." Clip art and "building block" illustration packs made with Macpaint soon put professional-looking graphics within reach of average users.

 
The marching ants around a selection; the palette of drawing tools; the (rudimentary) ability to zoom in; the spray can; the paint bucket; copying and pasting images between programs; just moving the mouse and drawing: we take these for granted in the 21st century, but Macpaint did them first, with only 128k of RAM available.

A generation of digital artists cut their teeth with this program well into the 1990s. Some still use it to achieve an "8-bit" style, while some pay homage to its famous built-in patterns with more modern software. See the contemporary gallery for examples of both.

These links can provide a very complete history of Macpaint:
-Andy Hertzfeld's fantastic account
-More from Andy Hertzfeld on the early use of Macpaint
-The Wikipedia article is surprisingly good
-The Computer History Museum
-Extensive Interview with Bill Atkinson and Andy Hertzfeld