I woke this morning to the sad news that GUI pioneer Bill Atkinson has passed away at age 74 from cancer. He is most well-known as a key member of the original Macintosh team alongside Steve Capps, Andy Hertzfeld, Burrell Smith, Bud Tribble, and others. But Atkinson’s work on GUIs predated the Mac: He was the lead developer and designer of the Apple Lisa, the first personal computer to offer a native GUI. And he is deservedly a legend. In addition to the the Lisa and Mac user interfaces, he created Apple Pascal, HyperCard, MacPaint, QuickDraw, and more.

The Lisa–and then the Mac–famously came about because Apple and Xerox had negotiated an Apple stock sale in exchange for demonstrations of Xerox PARC’s futuristic “humanized” technologies. Over two visits, ten Apple employees, including co-founder Steve Jobs and Atkinson, were shown several crucial advances: A mouse-driven GUI with a what-you-see-is-what-you-get (WYSIWYG) bitmapped display, a laser printer that provided pixel-perfect WYSIWYG output to paper, networking capabilities that linked two or more computers to each other to share files and printers, and SmallTalk, an object-oriented programming language. But Jobs was so excited by the GUI that he ignored the other capabilities, and he quickly directed to Lisa team to halt their efforts to create a 16-bit Apple II successor and refocus it on the GUI and mouse.

Atkinson didn’t need any prodding. Seeing PARC’s GUI for the first time, the programming prodigy had “examined each pixel so closely that [Xerox’s Larry] Tessler could feel the breath on his neck,” Walter Isaacson writes inSteve Jobs. When asked by Jobs during the car ride back to Apple from PARC how long it would take to implement a GUI, Atkinson told him “maybe six months.”

As with the Microsoft origin story that I discussed recently inTech Nostalgia: Microcomputer + Software (Premium), Atkinson’s achievements in the wake of that PARC visit are most impressive because they should have been impossible.

Atkinson had an advantage, however: He was a genius who had been lured to the company by Steve Jobs, who told him in 1978 that he should “come to Apple where you can invent the future and change millions of people’s lives.” He did just that with the Lisa and, later, the Mac. Not only did he quickly pull together a working GUI on the Lisa, but he also somehow managed to exceed the capabilities of the GUI that PARC had demonstrated.

As with the Xerox Star, the Lisa GUI utilized a desktop metaphor with on-screen icons and menus. Clicking an icon with a mouse opened a window, which visually appeared to be in front of the desktop. But Atkinson expanded on that design by adding crucial capabilities that are still common today, including drag and drop–the ability to select a window with the mouse and drag it to a new location on-screen–and window resizing.

Amazingly, one of Atkinson’s key contributions to this work was the result of a misunderstanding: He thought he had seen that the Xerox GUI supported overlapping windows, so he created a technology he calledregions that accomplished this visual effect on the underpowered Lisa too. But when the researchers at PARC saw what he had done later, they told Atkinson how amazed they were with the feature. It was so impressive thatApple patented the technique.

“Because I didn’t know it couldn’t be done,” Atkinson later said, “I was enabled to do it.”

Steve Jobs goaded Atkinson into other seemingly impossible achievements. After getting the basic GUI up and running with rectangular windows, he expanded his graphical routines–originally called LisaGraf before morphing into LisaDraw and then MacDraw–to draw ovals and circles.

“Bill had added new code to draw circles and ovals very quickly,”Andy Hertzfeld recalled. “That was a bit hard to do on the Macintosh, since the math for circles usually involved taking square roots, and the 68000 processor in the Lisa and Macintosh didn’t support floating point operations. But Bill had come up with a clever way to do the circle calculation that only used addition and subtraction, not even multiplication or division, which the 68000 could do, but was kind of slow at.”

Jobs was unimpressed. He asked Atkinson if he could also make “rectangles with rounded corners.” Atkinson told him this would be very difficult, if not impossible, and he didn’t see a reason to do so. But Jobs argued that rounded rectangles were everywhere, pointing to various objects in the room and outside the window that had that basic shape. And so Atkinson gave it a shot and surprised himself by figuring it out that night. He called the code he wrote RoundedRects. Hertzfeld said it could “draw rectangles with beautifully rounded corners blisteringly fast.”

Rounded rectangles quickly took over the Lisa GUI, and then the Mac, and it’s been an iconic part of Apple’s design philosophy ever since. Literally: The icons on the iPhone home screen are rounded rectangles and have been since that’s product’s inception in 2007.

RIP, Bill.