Hendrik Antoon Lorentz (18 July 1853 – 4 February 1928) was a Dutch theoretical physicist who shared the 1902 Nobel Prize in Physics with Pieter Zeeman for their discovery and theoretical explanation of the Zeeman effect. He derived the Lorentz transformation of the special theory of relativity, as well as the Lorentz force, which describes the force acting on a charged particle in an electromagnetic field. He was also responsible for the Lorentz oscillator model, a classical model used to describe the anomalous dispersion observed in dielectric materials when the driving frequency of the electric field was near the resonant frequency of the material, resulting in abnormal refractive indices.

Lorentz received many other honors and distinctions, including a term as Chairman of the International Committee on Intellectual Cooperation, the forerunner of UNESCO, from 1925 until his death in 1928.

Hendrik Antoon Lorentz was born on 18 July 1853 in Arnhem, Netherlands, the son of Gerrit Frederik Lorentz (1822–1893) and Geertruida van Ginkel (1826–1861). In 1862, after his mother's death, his father married Luberta Hupkes. Despite being raised as a Protestant, he was a freethinker in religious matters and regularly attended Catholic mass at his local French church.

From 1866 to 1869, Lorentz attended the Hogere Burgerschool in Arnhem, a new type of public high school recently established by Johan Thorbecke. His results in school were exemplary; not only did he excel in the physical sciences and mathematics, but also in English, French, and German. In 1870, he passed the exams in classical languages, which were then required for admission to university.

In 1870, Lorentz entered Leiden University, where he was strongly influenced by the teaching of astronomy professor Frederik Kaiser; it was his influence that led Lorentz to become a physicist. The following year, he obtained a B.Sc. in Mathematics and Physics. In 1872, he returned to Arnhem to become a night school teacher, while also continuing his studies at Leiden. In 1875, he received his Ph.D. under Pieter Rijke with a thesis on the reflection and refraction of light, in which he refined the electromagnetic theory of James Clerk Maxwell.

In 1878, Lorentz was appointed to the newly established Chair of Theoretical Physics at Leiden University; the position had initially been offered to Johannes van der Waals, but he had just accepted a professorship at the University of Amsterdam. On 25 January 1878, he delivered his inaugural lecture titled De moleculaire theoriën in de natuurkunde (The molecular theories in physics).

During his first 20 years at Leiden, Lorentz was primarily interested in the electromagnetic theory of electricity, magnetism, and light. After that, he extended his research to a much wider area while still focusing on theoretical physics. He made significant contributions to fields ranging from hydrodynamics to general relativity. His most important contributions were in the area of electromagnetism, the electron theory, and relativity.

In 1910, Lorentz decided to reorganize his career; his teaching and management duties at Leiden University were taking up too much of his time, leaving him little time for research. He initially asked Albert Einstein to succeed him as Professor of Theoretical Physics at Leiden. However, Einstein did not accept, because he had just taken up a position at ETH Zurich and the prospect of having to fill Lorentz's shoes made him shiver. He ultimately chose Paul Ehrenfest as his successor.