Mihailo Petrović Alas (Serbian Cyrillic: Михаило Петровић Алас; 6 May 1868 – 8 June 1943), was an influential Serbian mathematician and inventor. He was also a distinguished professor at Belgrade University, an academic, fisherman, writer, publicist, musician, businessman, traveler and volunteer in the First and Second World Wars. He was a student of Henri Poincaré, Paul Painlevé, Charles Hermite and Émile Picard. Petrović contributed significantly to the study of differential equations and phenomenology, as well as inventing one of the first prototypes of a hydraulic analog computer.^[1]

Petrović was born on 6 May 1868, in Belgrade, as the first child of Nikodim, a professor of theology, and Milica (née Lazarević).

He finished the First Belgrade Gymnasium in 1885, and afterwards enrolled at the natural science-mathematical section of the Faculty of Philosophy in Belgrade. At the time when he finished his studies in Serbia in 1889, several Serbian mathematicians who had acquired their doctorate degrees abroad, like Dr. Dimitrije Nešić (at Vienna and Karlsruhe Institute of Technology), Dr. Dimitrije Danić (at Jena, 1885) and Bogdan Gavrilović (at Budapest, 1887) were beginning to make a name for themselves. Subsequently, in September 1889, he too went abroad, to Paris to receive further education, and to prepare for the entrance exam to the École Normale Supérieure. He got a degree in mathematical sciences from Sorbonne University in 1891. He worked on preparing his doctoral dissertation, and on 21 June 1894 he defended his PhD degree at the Sorbonne, and received a title Docteur des sciences mathematiques (doctor of mathematical sciences). His doctorate was in the field of differential equations.

In 1894, Petrović became a professor of mathematics at the Belgrade's Grande école (which later became the University of Belgrade). In those days, he was one of the greatest experts for differential equations. He held lectures until his retirement in 1938. In 1897, he became an associate member of the Serbian Royal Academy and associate member of the Yugoslav Academy of Sciences and Arts in Zagreb. He became a full member of the Serbian Royal Academy in 1899, when he was only 31.

He was very interested in fishery, and thus his nickname, Alas (river fisherman). In 1882, he became a fisherman apprentice, and in 1895 he took the exam for master fisherman. He played violin, and in 1896, founded musical society named Suz. Mihailo Petrović Alas also constructed a hidrointegrator, and won the gold medal at the World Exposition in Paris 1900. When in 1905 the Grande école was transformed into the University of Belgrade Petrović was among first eight regular professors, who elected other professors.

He published a large number of inventions, scientific works, books and journals from his sea expeditions. He received numerous awards and acknowledgments and was a member of several foreign science academies (Prague, Bucharest, Warsaw, Kraków) and scientific societies. In 1927, when Jovan Cvijić died, members of the Serbian academy proposed Mihailo Petrović as the new president of academy, but the authorities did not accept this proposal. Probable reason for this was the fact that Mihailo Petrović Alas was first a private tutor and mentor and later a close friend of the prince Đorđe P. Karađorđević, the king's brother, who was arrested in 1925, and held in house arrest. In fact, the "close friendship" has been alleged to have included erotic involvement, so the father, King Peter I of Serbia accused Petrović in a private conversation of "stamping from behind" (in Serbian "печати одостраг", to wit: having anal intercourse with) Đorđe when the latter was a Crown Prince.^[2] The King was also upset when he read in a Belgrade journal that Petrović had written to prince Đorđe a personal letter signed with "Your dog on a chain", stating that "a man of integrity is not supposed to send such letters to a mere boy".^[3]

In 1931, members of the academy unanimously proposed Alas for the president of the academy, but authorities again dismissed this proposal. Mathematician and physicist Bogdan Gavrilović, a fellow professor, was nominated instead. In 1939, he became an honorary doctor at the University of Belgrade. In the same year, he received the order of Saint Sava, first class. He also founded the Belgrade School of Mathematics, which produced a number of mathematicians who continued Alas's work. All doctoral dissertations defended on the Belgrade University since 1912 until the Second World War were under his mentorship.

He participated in the Balkan Wars and in the First World War as an officer, and after the war he served as a reserve officer. He practised cryptography, and his cipher systems were used by the Yugoslav army until World War II. When the Second World War broke out in Yugoslavia, he was again called into the army and the Germans captured him. After a while, he was released because of illness. On 8 June 1943, professor Petrović died in his home in Kosančićev Venac Street in Belgrade.

He was a passionate traveller, and he visited both the North and South poles. Mihailo Petrović got the nickname "Alas" because of his passion for fishery. He was not only an aficionado, but expert as well. He participated in legislative talks regarding the fishery convention with Romania, and in talks with Austria-Hungary about the protection of the fishery on Sava, Drina and Danube rivers.

Ninth Belgrade Gymnasium "Mihailo Petrović Alas" and Primary School in John's Street is a high school in Belgrade, Serbia named after him.