Boris Kirilov Christoff was born in Plovdiv, Bulgaria, on May 18, 1914. Educated as a lawyer, he was heard by Bulgaria's King Boris while singing in the famous Gusla Choir. The King granted a scholarship to allow him to travel to Rome for voice studies. There, Christoff's teacher was Riccardo Stracciari. He then traveled to Salzburg for further studies. At the end of World War II, after spending time in a Nazi labor camp, he was a refugee. He traveled again to Rome, where he made a debut in a concert. His first operatic performance was in the role of Colline in Puccini's La bohème; this was in Reggio Calabria. His first appearance in the opera with which would become most associated, Mussorgsky's Boris Godunov, was in the year 1947, when he sang the part of Pimen in Rome and in La Scala. He made his first appearances in the title role in 1949 at Covent Garden. He sang the role in most of the major opera houses of the world; it was also his debut role in the United States, at the San Francisco Opera House on September 25, 1956. In the United States he was particularly associated with the Chicago Lyric Opera from 1957 to 1963. His brother-in-law, incidentally, was another great bass, Tito Gobbi.
As a Slavic singer with something of a specialty in Boris, he was inevitably compared with the Russian bass Feodor Chaliapin. He was also a formidable stage actor, thereby bringing his roles special dramatic depth. His voice was beautifully controlled, round, and full-sounding, although it was not a big voice. He was able to make great dramatic use of excellent projection and outstanding tonal qualities in soft singing, the quality most often praised following his legendary performance at Covent Garden as King Philip II of Spain in Verdi's Don Carlos. Unlike Chaliapin, he also built a major reputation as a Verdian bass in addition to specializing in the Russian composers. He also made his mark in the major Wagnerian bass roles such as Hagen (Götterdämmerung), Gurnemanz (Parsifal), and King Marke (Tristan und Isolde) but sang as far afield as Rocco in Beethoven's Fidelio and the title role of Handel's Giulio Cesare. He recorded many of his major roles. He also maintained a notable career as a recital singer, and recorded a wide range of the songs of the Russian Romantic-era composers.