Until his final years, Wagner's life was characterized by political exile, turbulent love affairs, poverty and repeated flight from his creditors. His controversial writings on music, drama and politics have attracted extensive comment since the late 20th century, especially where they express antisemitic sentiments. The effect of his ideas can be traced in many of the arts throughout the 20th century; his influence spread beyond composition into conducting, philosophy, literature, the visual arts and theater.
Wagner began composing the music for Das Rheingold between November 1853 and September 1854, following it immediately with Die Walküre (written between June 1854 and March 1856). He began work on the third Ring opera, which he now called simply Siegfried, probably in September 1856, but by June 1857 he had completed only the first two acts. He decided to put the work aside to concentrate on a new idea: Tristan und Isolde, based on the Arthurian love story Tristan and Iseult.
One source of inspiration for Tristan und Isolde was the philosophy of Arthur Schopenhauer, notably his The World as Will and Representation, to which Wagner had been introduced in 1854 by his poet friend Georg Herwegh. Wagner later called this the most important event of his life.
A second source of inspiration was Wagner's infatuation with the poet-writer Mathilde Wesendonck, the wife of the silk merchant Otto Wesendonck. Wagner met the Wesendoncks, who were both great admirers of his music, in Zürich in 1852. From May 1853 onwards Wesendonck made several loans to Wagner to finance his household expenses in Zürich, and in 1857 placed a cottage on his estate at Wagner's disposal,which became known as the Asyl ("asylum" or "place of rest"). During this period, Wagner's growing passion for his patron's wife inspired him to put aside work on the Ring cycle (which was not resumed for the next twelve years) and begin work on Tristan. While planning the opera, Wagner composed the Wesendonck Lieder, five songs for voice and piano, setting poems by Mathilde. Two of these settings are explicitly subtitled by Wagner as "studies for Tristan und Isolde".
Amongst the conducting engagements that Wagner undertook for revenue during this period, he gave several concerts in 1855 with the London Philharmonic Society, including one before Queen Victoria. The Queen enjoyed his Tannhäuser overture and spoke with Wagner after the concert, writing of him in her diary that he was "short, very quiet, wears spectacles & has a very finely-developed forehead, a hooked nose & projecting chin."
Wagner's uneasy affair with Mathilde collapsed in 1858, when his wife Minna intercepted a letter to Mathilde from him. After the resulting confrontation with Minna, Wagner left Zürich alone, bound for Venice, where he rented an apartment in the Palazzo Giustinian, while Minna returned to Germany. Wagner's attitude to Minna had changed; the editor of his correspondence with her, John Burk, has said that she was to him "an invalid, to be treated with kindness and consideration, but, except at a distance, a menace to his peace of mind." Wagner continued his correspondence with Mathilde and his friendship with her husband Otto, who maintained his financial support of the composer. In an 1859 letter to Mathilde, Wagner wrote, half-satirically, of Tristan: "Child! This Tristan is turning into something terrible. This final act!!!—I fear the opera will be banned ... only mediocre performances can save me! Perfectly good ones will be bound to drive people mad."
After grave difficulties in rehearsal, Tristan und Isolde premiered at the National Theatre Munich on 10 June 1865, the first Wagner opera premiere in almost 15 years. (The premiere had been scheduled for 15 May, but was delayed by bailiffs acting for Wagner's creditors, and also because the Isolde, Malvina Schnorr von Carolsfeld, was hoarse and needed time to recover.) The conductor of this premiere was Hans von Bülow, whose wife, Cosima, had given birth in April that year to a daughter, named Isolde, a child not of Bülow but of Wagner.
Minna had died of a heart attack on 25 January 1866 in Dresden. Wagner did not attend the funeral. Following Minna's death Cosima wrote to Hans von Bülow on a number of occasions asking him to grant her a divorce, but Bülow refused to concede this. He only consented after she had two more children with Wagner; another daughter, named Eva, after the heroine of Meistersinger, and a son Siegfried, named for the hero of the Ring. The divorce was finally sanctioned, after delays in the legal process, by a Berlin court on 18 July 1870. Richard and Cosima's wedding took place on 25 August 1870. On Christmas Day of that year, Wagner arranged a surprise performance (its premiere) of the Siegfried Idyll for Cosima's birthday. The marriage to Cosima lasted to the end of Wagner's life.