**Fejér**'s main work was in harmonic analysis working on Fourier series and their singularities. Fejér collaborated to produce important papers with Carathéodory on entire functions and with Riesz on conformal mappings.

- Weiss in German means "white" while the Hungarian for white is "feher" but he chose the name "Fejér" which is an archaic spelling for the Hungarian for "White".
- In that year Fejér entered the Polytechnic University of Budapest where he studied mathematics and physics until 1902, except for the year 1899-1900 which he spent at the University of Berlin.
- In Berlin he attended courses by Georg Frobenius and Lazarus Fuchs but it was his discussions with Hermann Schwarz that led him look at the convergence of Fourier series and prove the highly significant "Fejér's theorem" published in Sur les fonctions bornées et intégrables Ⓣ(On bounded and integrable functions).
- Also, at that time the theory of functions of one real variable had produced a number of strange anomalies (like continuous, nowhere differentiable functions), and Fejér's theorem, by its simplicity, reassured mathematicians who were disturbed by these pathological results.
- While attending Schwarz's twice-monthly colloquium, in which he was lecturing on his collected works, Fejér met Constantin Carathéodory, Erhard Schmidt and Issai Schur who were doctoral students, and Edmund Landau who was a privatdozent.
- From Schwarz, in addition to specific ideas for his research, Fejér inherited a geometrical approach to mathematics and a love of extremal problems.
- We note that it was while he was in Berlin that he changed his name from Weiss to Fejér and, after he did so, Schwarz jokingly refused to talk to him! Fejér's fundamental summation theorem for Fourier series formed the basis of his doctoral thesis which he presented to the University of Budapest in 1902.
- Fejér spent the winter of 1902-3 on a visit to Göttingen, attending lectures by David Hilbert and Hermann Minkowski, and the summer of 1903 in Paris where he attended lectures by Émile Picard and Jacques Hadamard.
- Although Fejér had gained an international reputation because of his outstanding papers, he did not have a permanent position in Hungary and was relatively unknown there.
- In 1911 Fejér was appointed to the chair of mathematics at the University of Budapest and he held that post until his death.
- One of them, knowing full well that Fejér's original name had been Weiss, asked during the occasion of Fejér's candidacy: 'Is this Leopold Fejér related to our distinguished colleague on the Faculty of Theology, Father Ignatius Fejér?' Without missing a beat Loránd Eötvös, Professor of Physics, answered "Illegitimate son".
- Despite these difficulties, Fejér was honoured with election to the Hungarian Academy of Sciences in 1911 and being a vice-president of the International Congress of Mathematicians held in Cambridge, England, in August 1912.
- During his period in the chair at Budapest, Fejér led a highly successful Hungarian school of analysis.
- Fejér's main work was in harmonic analysis.
- The hours spent in continental coffee houses with Fejér discussing mathematics and telling stories are a cherished recollection for many of us.
- Fejér presented his mathematical remarks with the same verve as his stories, and this may have helped him in winning the lasting interest of so many younger men in his problems.
- Yet he would not appear so in his natural habitat, in a certain section of Budapest middle-class society, many members of which had the same manners, if not quite the same mannerisms, as Fejér - there he would appear about half eccentric.
- We have already mentioned some of the honours given to Fejér but, in addition, he received the Kossuth Prize, first grade (1948), the People's Order of Merit (1950), and the Labour Red Flag of Merit (1953).
- There were, however, two factors whose influence on Hungarian mathematics is manifest and undeniable, and one of these was Leopold Fejér, his work, his personality.

Born 9 February 1880, Pécs, Hungary. Died 15 October 1959, Budapest, Hungary.

View full biography at MacTutor

Origin Hungary

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive