Who was Mathilde Wesendonk and how did she influence Tristan und Isolde?

Mathilde Wesendonk was the wife of a wealthy patron who supported Richard Wagner during his time in Zürich.1

Her influence on Tristan und Isolde was profound, as Wagner’s "hopeless love" for her served as the primary "crystallizing agent" for the opera’s composition between 1857 and 1859. This intense personal connection, which ultimately contributed to the separation between Wagner and his wife, Minna, occurred as Wagner’s philosophical outlook shifted from optimistic social theories toward the world-renouncing pessimism of Arthur Schopenhauer.1

This combination of personal emotional turmoil and Schopenhauer’s influence led Wagner to evolve his musical style. In Tristan und Isolde, he moved away from using leitmotifs primarily to explain dramatic action, instead employing them with greater psychological complexity through a method of free association.1