August Emil Daniel Ferdinand Wilhelmj ( [vɪlˈhɛlmi]; 21 September 1845 in Usingen – 22 January 1908 in London) was a German violinist and teacher.
Wilhelmj was considered a child prodigy. When Henriette Sontag heard him in 1852, when he was seven, she said "You will be the German Paganini". In 1861, Franz Liszt heard him and sent him to Ferdinand David with a letter containing the words "Let me present you the future Paganini!". His teachers included: Ferdinand David, for the violin, Moritz Hauptmann, for music theory and composition, and Joachim Raff for composition.
A personal friend of Wagner, he led the violins at the première of Der Ring des Niebelungen in Bayreuth in 1876. He visited Australia in 1881, playing in the old Freemasons' Hall, but though appreciated by those who attended his concerts, their number was not sufficient to make the tour a financial success. It was not until introduced to London audiences by Jenny Lind in 1886 that Wilhelmj became a "household name".
He has become famous for his late nineteenth century arrangement of the second movement of J. S. Bach's Orchestral Suite No. 3 for violin and piano, known as Air on the G String and for his re-orchestration of the 1st movement of Niccolò Paganini's Violin Concerto No.1 in D major Op.6 (1883/84).
From 1894 on he was a Professor of violin at the Guildhall School of Music and Drama. Among his pupils were American violinist Nahan Franko, Canadian musician Donald Heins, and the Australian conductor Aylmer Buesst. Wilhelmj owned a Stradivarius 1725 violin from 1866 until his retirement, which later came to be known by his name. His 1785 Guadagnini was later owned (as "ex-Wilhelmj") by Jack Liebeck.