Peter Gustav Lejeune Dirichlet
![](/Images/godic/202501/09/Peter_Gustav_Lejeune_Dirichlet1944.jpg")
![Dirichlet was married from 1832 to Rebecka Mendelssohn. They had two children, Walter (born 1833) and Flora (born 1845). Drawing by Wilhelm Hensel, 1823](/Images/godic/202501/09/Rebecka_Mendelssohn_-_Zeichnung_von_Wilhelm_Hensel_18231944.jpg")
![Dirichlet found and proved the convergence conditions for Fourier series decomposition. Pictured: the first four Fourier series approximations for a square wave.](/Images/godic/202501/09/Fourier_Series.svg1944.png")
Johann Peter Gustav Lejeune Dirichlet (German:[ləˈʒœn diʀiˈkleː] or [ləˈʒœn diʀiˈʃleː]; 13 February 1805 – 5 May 1859) was a German mathematician who made deep contributions to number theory (including creating the field of analytic number theory), and to the theory of Fourier series and other topics in mathematical analysis; he is credited with being one of the first mathematicians to give the modern formal definition of a function.