Answer by taking a quote from the following article:

Daniel Barenboim (born 15 November 1942) is an Argentine-Israeli pianist and conductor who is a citizen of Argentina, Israel, Palestine, and Spain. He is the general music director of the Berlin State Opera, and the Staatskapelle Berlin; he previously served as Music Director of the Chicago Symphony Orchestra, the Orchestre de Paris and La Scala in Milan. Barenboim is known for his work with the West-Eastern Divan Orchestra, a Seville-based orchestra of young Arab and Israeli musicians, and as a resolute critic of the Israeli occupation of Palestinian territories. Barenboim has received many awards and prizes, including an honorary Knight Commander of the Order of the British Empire, France's Legion d'honneur both as a Commander and Grand Officier, and the German Grosses Bundesverdienstkreuz and Willy Brandt Award.

Daniel Barenboim was born in 1942 in Buenos Aires, Argentina, to Argentinian-Jewish parents Aida (nee Schuster) and Enrique Barenboim. He started piano lessons at the age of five with his mother, continuing to study with his father, who remained his only teacher. On 19 August 1950, at the age of seven, he gave his first formal concert in his hometown, Buenos Aires.  In 1952, Barenboim's family moved to Israel. Two years later, in the summer of 1954, his parents took him to Salzburg to take part in Igor Markevitch's conducting classes. During that summer he also met and played for Wilhelm Furtwangler, who has remained a central musical influence and ideal for Barenboim. Furtwangler called the young Barenboim a "phenomenon" and invited him to perform the Beethoven First Piano Concerto with the Berlin Philharmonic, but Barenboim's father considered it too soon after the Second World War for a child of Jewish parents to be performing in Berlin. In 1955 Barenboim studied harmony and composition with Nadia Boulanger in Paris.  On 15 June 1967, Barenboim and British cellist Jacqueline du Pre were married in Jerusalem at a Western Wall ceremony, Du Pre having converted to Judaism. Acting as one of the witnesses was the conductor Zubin Mehta, a long-time friend of Barenboim. Since "I was not Jewish I had to temporarily be renamed Moshe Cohen, which made me a 'kosher witness'," Mehta recalled. Du Pre retired from music in 1973, after being diagnosed with multiple sclerosis (MS). The marriage lasted until du Pre's death in 1987.  In the early 1980s, Barenboim began an affair with the Russian pianist Elena Bashkirova, with whom he had two sons born in Paris before du Pre's death: David Arthur, born 1983, and Michael, born 1985. Barenboim worked to keep his relationship with Bashkirova hidden from du Pre, and believed he had succeeded. He and Bashkirova married in 1988. Both sons are part of the music world: David is a manager-writer for the German hip-hop band Level 8, and Michael Barenboim is a classical violinist.

What did Wilhelm Furtwangler teach him?
Furtwangler called the young Barenboim a "phenomenon" and invited him to perform the Beethoven First Piano Concerto with the Berlin Philharmonic,