Stephen Gary Wozniak (/ˈwɒzniæk/; born August 11, 1950), also known by his nickname Woz, is an American technology entrepreneur, electrical engineer, computer programmer, and inventor. In 1976, he co-founded Apple Computer with his early business partner Steve Jobs. Through his work at Apple in the 1970s and 1980s, he is widely recognized as one of the most prominent pioneers of the personal computer revolution.

In 1975, Wozniak started developing the Apple I into the computer that launched Apple when he and Jobs first began marketing it the following year. He was the primary designer of the Apple II, introduced in 1977, known as one of the first highly successful mass-produced microcomputers, while Jobs oversaw the development of its foam-molded plastic case and early Apple employee Rod Holt developed its switching power supply.

With human–computer interface expert Jef Raskin, Wozniak had a major influence over the initial development of the original Macintosh concepts from 1979 to 1981, when Jobs took over the project following Wozniak's brief departure from the company due to a traumatic airplane accident. After permanently leaving Apple in 1985, Wozniak founded CL 9 and created the first programmable universal remote, released in 1987. He then pursued several other business and philanthropic ventures throughout his career, focusing largely on technology in K–12 schools, which involved a 1990 initiative to place computers in schools in the former Soviet Union.

He has received numerous awards and honors for his work in philanthropy and the tech industry, including an induction into the National Inventors Hall of Fame in 2000. As of June 2024, Wozniak has remained an employee of Apple in a ceremonial capacity since stepping down in 1985. In recent years, he has helped fund multiple entrepreneurial efforts dealing in areas such as GPS and telecommunications, flash memory, technology and pop culture conventions, technical education, ecology, satellites and more. In addition to his American citizenship, Wozniak is also a Polish and Serbian citizen.

Stephen Gary Wozniak was born on August 11, 1950, in San Jose, California. His mother, Margaret Louise Wozniak (née Kern) (1923–2014), was from Washington state, and his father, Francis Jacob "Jerry" Wozniak (1925–1994) of Michigan, was an engineer for the Lockheed Corporation. Wozniak graduated from Homestead High School in 1968, in Cupertino, California. Steve has one brother, Mark, a former tech executive who lives in Menlo Park. He also has one sister, Leslie, who attended Homestead High School in Cupertino. She is a grant adviser at Five Bridges Foundation, which helps at-risk youths in San Francisco. Leslie said it was her mother who introduced activism to her and her siblings.

The name on Wozniak's birth certificate is "Stephan Gary Wozniak", but his mother said that she intended it to be spelled "Stephen", which is what he uses. Wozniak is of Polish and German ancestry. In the early 1970s, Wozniak's blue box design earned him the nickname "Berkeley Blue" in the phreaking community. Wozniak has credited watching Star Trek and attending Star Trek conventions while in his youth as a source of inspiration for his starting Apple Computer. In his autobiography, iWoz, he also credits the Tom Swift Jr. books as an inspiration for becoming an engineer.

In 1969, Wozniak returned to the San Francisco Bay Area after being expelled from the University of Colorado Boulder in his first year for hacking the university's computer system. He re-enrolled at De Anza College in Cupertino before transferring to the University of California, Berkeley, in 1971. In June of that year, for a self-taught engineering project, Wozniak designed and built his first computer with his friend Bill Fernandez.

Predating useful microprocessors, screens, and keyboards, and using punch cards and only 20 TTL chips donated by an acquaintance, they named it "Cream Soda" after their favorite beverage. A newspaper reporter stepped on the power supply cable and blew up the computer, but it served Wozniak as "a good prelude to my thinking 5 years later with the Apple I and Apple II computers". Before focusing his attention on Apple, he was employed at Hewlett-Packard (HP), where he designed calculators. It was during this time that he dropped out of Berkeley and befriended Steve Jobs.