Karl Ridderbusch (29 May 1932 – 21 June 1997) was a German operatic bass, associated in particular with the music of Wagner. He was recognised as a notable exponent of the role of Hans Sachs.
Karl Ridderbusch was born in Recklinghausen, Germany, and was discovered at an amateur music competition by the tenor Rudolf Schock who helped pay for the younger singer's training. Ridderbusch had previously planned to work as an engineer for his father. After studying at the conservatoire in Duisburg and the Folkwang Hochschule in Essen, he made his debut at the State Theatre in Münster in 1961. Roles he sang there included the Commendatore and Phillip II. Ridderbusch's next post was in Essen where he added major roles by Verdi, Strauss and Wagner to his repertoire. In 1965, he joined the Deutsche Oper am Rhein, where he was based for the rest of his career. Roles there included Phillip II, Henry VIII,Sparafucile, Boris Godunov and Hunding.
Ridderbusch's voice ranged over two octaves, allowing him to sing bass-baritone roles, such as Hans Sachs and Don Pizarro, and not just bass parts. Its qualities have been described as "firm clear sonorous and rich in timbre" and as "magnificently resonant [and] dark-coloured". He was known for his ability to maintain beauty of tone even at his loudest. He also had a formidable stage presence.