Question: Who was mentor to the man whose works, along with those of Alban Berg, were included in the studio album entitled At the Grave of Richard Wagner?

Context paragraphs:
Hildegard Behrens: Hildegard Behrens (9 February 1937 – 18 August 2009) was a German soprano with a wide repertoire including Wagner, Weber, Mozart, Richard Strauss, and Alban Berg roles.

Victor Braun: Victor Conrad Braun (August 4, 1935 – January 6, 2001) was a Canadian baritone who had a major international performance career in concerts and operas that lasted more than 40 years.  While he was an accomplished performer of the standard opera works of Mozart, Puccini, Strauss, Verdi, and Wagner; he was particularly lauded for his portrayals of works by 20th-century composers like Alban Berg, Bartók, Henze, Siegfried Matthus, and Luciano Berio among others.

Rogelio de Egusquiza: Rogelio de Egusquiza y Barrena (1845, El Astillero - 10 February 1915, Madrid) was a Spanish painter, known for his friendship with the German composer Richard Wagner, whose works he helped make familiar in Spain.

Siegfried Lipiner: Siegfried Salomo Lipiner (24 October 1856 – 30 December 1911) was an Austrian writer and poet whose works made an impression on Richard Wagner and Friedrich Nietzsche, but who published nothing after 1880 and lived out his life as Librarian of Parliament in Vienna.  A poet and dramatist of highly individual character, he is today remembered in German-speaking literary circles mainly for his translations of the Polish poet Adam Mickiewicz; he is also known to music history as having been a close friend of Gustav Mahler.

At the Grave of Richard Wagner: At the Grave of Richard Wagner is a studio album by the Kronos Quartet, containing works by Alban Berg and Anton Webern, and a brief "romantic elegy" by Franz Liszt.

Mandisa discography: This is a discography of Mandisa, an African-American gospel and contemporary Christian artist.  In her career she has released three studio albums, including one Christmas album, and one EP.  Her first album "True Beauty" debuted at number one on the Top Christian Albums chart, and at number 47 on the Billboard Top 200.  She also released a Christmas EP entitled "Christmas Joy" on November 20, 2007.  In 2008, she released her second studio album, a full length Christmas album, entitled "It's Christmas", debuting at number 37 on the Top Christian Albums chart, and at number 44 on the Top Holiday Albums.  In 2009, she released her third full-length studio album entitled "Freedom".  On April 5, 2011 she released her fourth studio album, "What If We Were Real".

Seven Early Songs (Berg): The Seven Early Songs ("Sieben frühe Lieder") (c. 1905 – 1908), are early compositions of Alban Berg, written while he was under the tutelage of Arnold Schoenberg.  They are an interesting synthesis combining Berg's heritage of pre-Schoenberg song writing with the rigour and undeniable influence of Schoenberg.  The writing very much carries with it the heritage of Richard Strauss (although the influences of a number of other composers can be discerned – Gustav Mahler and Hugo Wolf for example, as well as Claude Debussy's harmonic palette in evidence in "Nacht"), through the expansiveness of gesture and 'opening of new vistas,' and that of Richard Wagner.  The songs were first written for a medium voice and piano; they were revised for high voice and orchestra in 1928.

Rheingold (Grave Digger album): Rheingold is the 11th studio album by German band Grave Digger.  It is a concept album based on Richard Wagner's "The Ring of the Nibelung".  The album was released in 2003.  Many lines of the lyrics are quoted or paraphrased from (an English translation of) Wagner.  The music also has occasional references to Wagner, the most obvious one perhaps being the intro to the song "Dragon", which is the "Siegfried's Horn Call" leitmotif.

Anton Webern: Anton Friedrich Wilhelm (von) Webern (] ; 3 December 188315 September 1945) was an Austrian composer and conductor.  Along with his mentor Arnold Schoenberg and his colleague Alban Berg, Webern was at the core among those within and more peripheral to the circle of the Second Viennese School, including Ernst Krenek and Theodor W. Adorno.  As an exponent of atonality and twelve-tone technique, Webern exerted influence on contemporaries Luigi Dallapiccola, Křenek, and even Schoenberg himself.  As a tutor, Webern guided and variously influenced Arnold Elston, Frederick Dorian (Friederich Deutsch), Matty Niël, Fré Focke, Karl Amadeus Hartmann, Philipp Herschkowitz, René Leibowitz, Humphrey Searle, Leopold Spinner, and Stefan Wolpe.

Anne Schwanewilms: Anne Schwanewilms (born 1967, in Gelsenkirchen) is a German lyric soprano.  She studied gardening before training in Cologne as a singer with the German bass Hans Sotin.  She is particularly associated with performing the works of Richard Wagner, Franz Schreker, Alban Berg, and Richard Strauss.  She sang the lead role of Carlotta in Franz Schreker's "Die Gezeichneten" at the Salzburg Festival in 2005, recorded and subsequently published on DVD by Opus Arte.

Supporting paragraphs: At the Grave of Richard Wagner Anton Webern
Answer: Arnold Schoenberg