Sir Charles Kuen Kao (November 4, 1933 – September 23, 2018) was a Hong Kong electrical engineer who contributed to the development and use of fibre optics in telecommunications. In the 1960s, Kao created various methods to combine glass fibres with lasers in order to transmit digital data, which laid the groundwork for the evolution of the Internet and the eventual creation of the World Wide Web.

Born in 1933 in Shanghai, Kao and his family settled in Hong Kong in 1949. He graduated from St. Joseph's College in Hong Kong in 1952 and went to London to study electrical engineering. In the 1960s, he worked at Standard Telecommunication Laboratories, the research center of Standard Telephones and Cables (STC) in Harlow, and it was here in 1966 that he laid the groundwork for fibre optics in communication. Known as the "godfather of broadband," the "father of fibre optics," and the "father of fibre optic communications," he continued his work in Hong Kong at the Chinese University of Hong Kong, and in the United States at ITT (the parent corporation of STC) and Yale University.

In 2009, Kao was awarded the Nobel Prize in Physics "for groundbreaking achievements concerning the transmission of light in fibres for optical communication." The following year, he was knighted by Queen Elizabeth II "for services to fibre-optic communications."

Kao was a permanent resident of Hong Kong, and a citizen of the United Kingdom and the United States. that was founded by a number of progressive Chinese educators, including Cai Yuanpei.

After the Communist Revolution in 1949, Kao's family settled in Hong Kong, which at the time was a British crown colony. Much of his mother's siblings moved to Hong Kong in the late 1930s. Among them, his mother's youngest brother took good care of him.

Kao's family lived on Lau Sin Street at the edge of the North Point, a neighbourhood of Shanghai immigrants.

Kao obtained high score in the Hong Kong School Certificate Examination, which at the time was the territory's matriculation examination, qualifying him for admission to the University of Hong Kong (HKU). However, electrical engineering wasn't a programme available at HKU, the territory's then only tertiary education institution. He then pursued research and received his Ph.D. in Electrical Engineering in 1965 from the University College London—under the supervision of Harold Barlow—as an external student while working at Standard Telecommunication Laboratories in Harlow, the research centre of Standard Telephones and Cables (STC). He was a judge at the Shanghai Concession and later a professor at Soochow University (then in Shanghai) Comparative Law School of China.

His grandfather Kao Hsieh was a scholar, poet, and artist. Several writers including Kao Hsü, (), and () were also Kao's close relatives.

His father's cousin was astronomer Kao Ping-tse (Kao crater is named after him). Kao's younger brother Timothy Wu Kao () is a civil engineer and professor emeritus at the Catholic University of America; his research is in hydrodynamics.

Kao met his future wife Gwen May-Wan Kao (née Wong; ) in London after graduation, when they worked together as engineers at STC. She was British Chinese. They were married in 1959 in London, and had a son and a daughter, both of whom reside and work in Silicon Valley, California. According to Kao's autobiography, Kao was a Catholic who attended Catholic Church while his wife attended the Anglican Communion.]]

In the 1960s at Standard Telecommunication Laboratories (STL) based in Harlow, Essex, England, Kao and his coworkers did their pioneering work in creating fibre optics as a telecommunications medium, by demonstrating that the high-loss of existing fibre optics arose from impurities in the glass, rather than from an underlying problem with the technology itself.

In 1963, when Kao first joined the optical communications research team he made notes summarising the background situation and available technology at the time, and identifying the key individuals Later that year, Kao was appointed head of the electro-optics research group at STL. He took over the optical communication program of STL in December 1964, because his supervisor, Karbowiak, left to take the chair in Communications in the School of Electrical Engineering at the University of New South Wales (UNSW), Sydney, Australia.

Although Kao succeeded Karbowiak as manager of optical communications research, he immediately decided to abandon Karbowiak's plan (thin-film waveguide) and overall change research direction with his colleague George Hockham. This study proposed the use of glass fibres for optical communication. The concepts described, especially the electromagnetic theory and performance parameters, are the basis of today's optical fibre communications.

In 1965,