Sir Alexander Blackie William Kennedy FRS, FRGS (17 March 1847 – 1 November 1928), better known simply as Alexander Kennedy, was a leading British civil and electrical engineer and academic. A member of many institutions and the recipient of three honorary doctorates, Kennedy was also an avid mountaineer and a keen amateur photographer being one of the first to document the archaeological site of Petra in Jordan following the collapse of the Ottoman Empire.

Kennedy was born in Stepney, London to Rev. John Kennedy, MA, and Helen Stodart Blackie, both from Aberdeen. His maternal uncle was John Stuart Blackie, a Scottish scholar. He received his early education at the City of London School, before taking a short course at the Royal School of Mines, Jermyn Street to give him a basic grounding in engineering. In 1864, he was apprenticed into the shipbuilding firm of J & W Dudgeon of Cubitt Town. He spent the next four years there working as a draughtsman and had a hand in the construction of the first ships with compound engines and twin screws. By the time he left in 1868 he was one of a few draughtsmen in the country with a thorough understanding of the workings of both systems. He put this understanding to good use when he joined Palmers' Engine Works of Jarrow on Tyne upon completion of his apprenticeship, he became the leading draughtsman and designed the first compound engine to be built in the north. Having spent three years with Palmers he worked for a short time for T.M. Tennant and Company of Leith as their chief draughtsman.

In 1871 at the young age of 24 he was invited to become a partner of H.O. Bennett in Edinburgh. Over the next three years Kennedy was heavily involved with boiler design, building and testing. In 1873 he visited the Vienna Exhibition to study the boiler and engine designs exhibited there. He wrote a series of articles on several designs for the journal Engineering which were later reprinted in the official report on the exhibition made by the British Royal Commission.

In 1874, aged only 27, he was appointed to the chair of Engineering at University College, London, a post he would hold for the next 15 years (succeeded by Thomas Hudson Beare). He set about a series of changes that were to reform the way engineering was taught worldwide. He insisted that all of his students received not only lectures in engineering principles but also a firm grounding in mathematics, physics, chemistry, geology and the other sciences upon which engineering is based. He also asked that an engineering laboratory be built so that the students could have first hand experience of the applications of their theoretical studies. This proposal met widespread support from the engineering profession and the presidents of the Institution of Civil Engineers and the Institution of Mechanical Engineers were among the leading figures who supported it. In 1878 the laboratory was built and put to use, it was the first of its kind in the world and proved so useful that over the next nine years ten other educational institutions followed Professor Kennedy's example and built their own.

Whilst working at the UCL he translated Franz Reuleaux's Theoretische Kinematik (1875, Vieweg und Sohn) into English for the first time in 1876 (with title The Kinematics of Machinery). In August 1876 Kennedy gave two lectures at South Kensington on the kinematics of machinery. In 1886, he published Mechanics of Machinery, the first time that a book based on Reuleaux's kinematic analysis had been published in English. He also used the laboratory to carry out experiments to determine the strength and elasticity of various materials and was elected as a fellow of the Royal Society for this work in 1887. There followed a series of other experiments in which he investigated the strength of riveted joints and the possibility of developing new electric turbines.

Kennedy found time outside of his academic works to establish an extensive consultancy business. His designs include the steel arched pier at Trouville-sur-Mer, the concrete structure and steelwork of the rebuilt Alhambra Theatre and the steelwork of the first Hotel Cecil. He made great use of his laboratory to test his materials and his designs were always valued for the hours of research he had invested in them. During this period he was asked to investigate a remote oil concession in California which lay several days horse riding from the nearest road or railway. Kennedy had no riding experience and knew little about horses, however he immediately accepted the job and set about arranging riding classes in the mornings before he started lecturing. He soon became a very proficient rider and the trip to California proved a great success for Kennedy and the concession owners.

In 1889, Kennedy resigned his professorship and left the University turning to electrical engineering, which he had researched during his academic career. That year he established a very thriving private practise as a consulting engineer at Westminster in partnership with Bernard Maxwell Jenkin, (son of Fleeming Jenkin) with the firm adopting the name of Kennedy & Jenkin. His consultancy soon became famous for its works in this field. His first major contract was to design the supply system for the Westminster Electric Supply Corporation and he was retained by that corporation as their consultant engineer for the rest of his life. He also worked for the Central Electric Company and the St James and Pall Mall Electric Light Company. Many towns first electric generating stations were built to his designs including those of Edinburgh, Glasgow, Manchester, Belfast, Croydon, Carlisle, Kirkcaldy, Weymouth, Hartlepool, York and Rotherham. Kennedy was contracted to build two hydroelectric stations for the British Aluminium Company, their first at Foyers in 1896 and a second at Kinlochleven in 1909.

Kennedy also acted as a consultant to several railway companies in the London area, particularly in regard to electrification and tram systems. He advised the London County Council with regard to their tram network and instigated their use of unusual underground conduits for their electricity supply. In 1896 he was appointed engineer to the Waterloo and City Railway and the electrical systems were designed to his specifications. He held consultancy contracts with the London and Home Counties Electricity Authority, London Power Company, Edinburgh Corporation and the Calcutta Electric Supply Corporation. Kennedy hired as his Assistant Engineer at the firm another climber, Sydney Donkin, who was made a partner in the business in 1908 and became senior partner in 1934 upon the retirement of the son of the founder. ^{[citation needed]}