The base-baritone Robert Koller performed a wide range of main solo roles including the role of King Cosroe in Siroe, Re di Persia by Haendel with the Venice Baroque Orchestra under the direction of Andrea Marcon which took him to perform at the Musikhalle Hamburg and at the Zellerbach Hall San Francisco as well as to make his soloist appearance with the Capella Reial de Catalunya under Jordi Savall at the Styriarte Graz, at the festival of Ambronay and at the Basilica of Vézelay.
In 2010, he got the lead part in "Extravagancia" at the Teatro Colón in Buenos Aires staged by R. Spregelburd and in "Nacht" by G.-F. Haas at the Lucerne Festival (KKL) in 2011.
Semperoper Dresden employed him the following year to sing the title role in "El Cimarron“ by H.-W. Henze.
2013 brought him as a soloist to the "Ittinger Pfingsttage" under Heinz Holliger, to the Grande Opéra de Genève with Kurtàgs' "pas à pas..."
and to sing the Missa Solemnis by Beethoven at the Wiener Musikverein.
Since 2014, Robert has been working under Heinz Holliger for the baritone cycle "Lunea" at the Alte Oper Frankfurt (world premiere of the orchestrated version) with the Ensemble Modern, broadcast by Radio Hessen (hr2). In the same year, he sang the baritone solo part in "Dunkle Spiegel“ conducted by Heinz Holliger at the Tonhalle Zürich.
In 2015, Robert's solos have been heard in Beethoven's Ninth at the Berliner Philharmonie, at Tonhalle Zürich under Heinz Holliger and at the Alte Oper Frankfurt under Emilio Pomárico.
In 2016 he will perform the baritone part in "sombre" by Kaija Saariaho at the Schwetzinger SWR Festspiele as well as the solo parts of "Walpurgisnacht" by Mendelssohn with the Tonhalle Orchester Zürich.