Douglas Carl Engelbart (January 30, 1925 – July 2, 2013) was an American engineer, inventor, and a pioneer in many aspects of computer science. He is best known for his work on founding the field of human–computer interaction, particularly while at his Augmentation Research Center Lab in SRI International, which resulted in creation of the computer mouse, and the development of hypertext, networked computers, and precursors to graphical user interfaces. These were demonstrated at The Mother of All Demos in 1968. Engelbart's law, the observation that the intrinsic rate of human performance is exponential, is named after him.

The "oN-Line System" (NLS) developed by the Augmentation Research Center under Engelbart's guidance with funding mostly from the Advanced Research Projects Agency (ARPA), later renamed Defense Advanced Research Projects Agency (DARPA), demonstrated many technologies, most of which are now in widespread use; it included the computer mouse, bitmapped screens, word processing, and hypertext; all of which were displayed at "The Mother of All Demos" in 1968. The lab was transferred from SRI to Tymshare in the late 1970s, which was acquired by McDonnell Douglas in 1984, and NLS was renamed Augment (now the Doug Engelbart Institute). At both Tymshare and McDonnell Douglas, Engelbart was limited by a lack of interest in his ideas and funding to pursue them and retired in 1986.

In 1988, Engelbart and his daughter Christina launched the Bootstrap Institute – later known as The Doug Engelbart Institute – to promote his vision, especially at Stanford University; this effort did result in some DARPA funding to modernize the user interface of Augment. In December 2000, United States President Bill Clinton awarded Engelbart the National Medal of Technology, the U.S.'s highest technology award. In December 2008, Engelbart was honored by SRI at the 40th anniversary of the "Mother of All Demos".

Engelbart was born in Portland, Oregon, on January 30, 1925, to Carl Louis Engelbart and Gladys Charlotte Amelia Munson Engelbart. His ancestors were of German, Swedish and Norwegian descent.

He was the middle of three children, with a sister Dorianne (three years older), and a brother David (14 months younger). The family lived in Portland, Oregon, in his early years, and moved to the surrounding countryside along Johnson Creek when he was 8. His father died one year later. He graduated from Portland's Franklin High School in 1942.

Midway through his undergraduate years at Oregon State University, he served two years in the United States Navy as a radio and radar technician in the Philippines. It was there, on the remote island of Leyte in a small traditional hut on stilts, that he read Vannevar Bush's article "As We May Think", which would have a large influence on his thinking and work. He returned to Oregon State and completed his bachelor's degree in electrical engineering in 1948. While at Oregon State, he was a member of Sigma Phi Epsilon social fraternity. He was hired by the National Advisory Committee for Aeronautics at the Ames Research Center, where he worked in wind tunnel maintenance. In his off hours he enjoyed hiking, camping, and folk dancing. It was there he met Ballard Fish (August 18, 1928 – June 18, 1997), who was just completing her training to become an occupational therapist. They were married in Portola State Park on May 5, 1951. Soon after, Engelbart left Ames to pursue graduate studies at the University of California, Berkeley. At Berkeley, he studied electrical engineering with a specialty in computers, earning his Master of Science (MS) in 1953 and his Doctor of Philosophy (PhD) in 1955.

Engelbart's career was inspired in December 1950 when he was engaged to be married and realized he had no career goals other than "a steady job, getting married and living happily ever after". Over several months he reasoned that:

In 1945, Engelbart had read with interest Vannevar Bush's article "As We May Think", a call to action for making knowledge widely available as a national peacetime grand challenge. He had also read something about the recent phenomenon of computers, and from his experience as a radar technician, he knew that information could be analyzed and displayed on a screen. He envisioned intellectual workers sitting at display "working stations", flying through information space, harnessing their collective intellectual capacity to solve important problems together in much more powerful ways. Harnessing collective intellect, facilitated by interactive computers, became his life's mission at a time when computers were viewed as number crunching tools.