[1] Thanks to a government grant, Christoff left in May 1942 for Italy where he was tutored for two years in the core Italian bass repertoire by the great baritone of an earlier generation, Riccardo Stracciari.

[3] Christoff made his operatic debut as Colline in La bohème at Reggio Calabria on 12 March 1946.

After the restrictions were loosened, Christoff made an operatic debut in the United States in 1956 at the San Francisco Opera.

[14] He brought his career to an end with a final concert at the Accademia di Bulgaria in Rome on 22 June 1986.

He died in Rome in 1993 and his body was returned to Bulgaria, lay in repose in St. Alexander Nevski Cathedral[10] and was buried in section 46 of Sofia Central Cemetery.

Although it was not as large as some other bass voices, he had no trouble making an impact in big spaces like the San Francisco Opera.

Owing to his stage presence and dramatic temperament, he was a worthy heir to the grand tradition of Slavonic basses exemplified by Fyodor Stravinsky, Lev Sibiriakov, Vladimir Kastorsky, Feodor Chaliapin, Alexander Kipnis and Mark Reizen, among others.

In 1952, he participated in the widely known recording of this opera in Paris, in which at the suggestion of the conductor Issay Dobrowen he performed all three bass roles—Boris Godunov, Varlaam and Pimen— three very diverse roles, which he distinguished characteristically and, according to musicologist Marcel Clavery, their only common feature was the beauty of the singer's timbre.

An EMI representative was sent for an audition in Sofia, who was convinced of Boris Hristov's judgement, and so the choir took part in the recording conducted by André Cluytens, called triumphal.

[18][19] While he was a grand performer on stage, Christoff had difficult off-stage relations with some fellow singers and producers, which sometimes grew into public scandals.

[20] In 1961 his contract with La Scala was terminated after an open conflict with fellow Bulgarian Nicolai Ghiaurov.