Bulgarian bass singer. His extraordinary stage presence and his distinctive, powerfully projected voice, with its astonishing range of colour and nuance, made him one of this century's greatest interpreters of Verdi and of Russian operas. He was known for roles such as Mussorgsky's Boris Godunov, Philip II in Verdi's Don Carlos, Ivan the Terrible in Rimsky-Korsakov's The Maid of Pskov, and the title role in Mefistofele/Mephistopheles by the Italian composer Arrigo Boito (1842–1918). His greater range is revealed in recordings of the complete songs of Mussorgsky.
Christoff was born in Plovdiv, the son of a teacher and keen amateur musician. He sang in the local children's choir and became fascinated by opera at the age of ten when he saw Weber's Der Freischutz at the National Opera in Sofia. At 18 he joined the famous Gussla Choir and continued to sing as an amateur after he had qualified as a lawyer. When the choir sang at the royal palace, King Boris III was so impressed with Christoff's solo that he arranged a scholarship for him to study in Italy, so Christoff went to Rome in 1942 to study with the baritone Riccardo Stracciari.
He made his professional debut at a concert at the Santa Cecilia Academy in 1946. The following year he sang in Puccini's La Bohème at the Teatro Argentina, Rome. His success led to engagements at La Fenice, Venice, and La Scala, Milan. His Covent Garden debut in 1949 was as Boris Godunov, which he was singing for the first time. He first sang Philip II in Florence in 1950 and sang the role again in the Lucino Visconti production at Covent Garden on 1958 with Tito Gobbi, his brother-in-law, as Rodrigo, and Carlo Maria Guilini conducting. He sang these roles several times at Covent Garden in the years that followed, and sang these and many other roles in most of the famous opera houses in Europe and the USA. He also performed on the recital platform, most notably in Russian song. Much of his art is preserved in recordings.