When you went to hear her sing, you always knew exactly what you would get. Sumptuous, creamy and voluptuous tone was Norman’s trademark, along with a meticulous attention to text and expression. For some, it was all too grand and undifferentiated, like a meal in which the richness of the food was overwhelming and unchanging in every course. But the sheer vocal splendour that Norman produced was the sort of sound that comes only once in a lifetime.

Yet Norman was not just an unforgettable voice. She was an unforgettable public presence – an African American presence – in every event in which she participated. The knowingness that marked her vocal art extended seamlessly to her public conduct. Her choices on Desert Island Discs did not include her own recordings (which, given her personality, they might easily have done) but Martin Luther King’s “I have a dream” speech. She was a majestic figure in every sense, and she knew from the start of her career to the end that she was also an embodiment of her black brothers and sisters. She would never be anybody’s second-class citizen. And she never was.

Norman was not the breakthrough African American singer of 20th-century America. Those imperishable accolades belonged to Marian Anderson and, a little later, to Leontyne Price, who each made the breaches in the whites-only world of classical music and opera. But she was in every way Price’s successor as the flag carrier for her people in the concert halls and opera houses of the US and the wider world. Like Price, she came from the south and developed her voice in church choirs. But, perhaps even more than Price, Norman embraced her iconic status in wider American life as an integral part of the gift she possessed.

Norman’s operatic career had to take account of both her vocal richness and her substantial height. She never possessed an athletic stage presence, and she was not really an ensemble actor. The roles that suited her best were often statuesque, where her character’s emotional presence was able to dominate. Her Elizabeth in Wagner’s Tannhäuser and, in particular her Cassandre in Berlioz’s Les Troyens, which she sang at Covent Garden, were characterisations of this kind.

Later, she excelled in the title role of Strauss’s Ariadne auf Naxos, to which the tragic dignity of her vocal breadth was perfectly suited. Though she sang Mozart with total commitment, her voice was simply too big and her personality too grand to fit into such quicksilver writing.

Stories of Norman’s imperious behaviour were common in the musical world. She could be uncompromising about the standards she expected from herself and others. And she was said to require to be collected in a Rolls Royce. But she never lost her lofty status as a great artist. When Herbert von Karajan, another difficult and imperious personality, was preparing for what was likely to be his final appearance at the Salzburg festival, it was Norman he wanted by his side, to sing Isolde’s Liebestod.

Concerts were Norman’s ideal milieu, especially as her career entered its final years. Her range was great. She sang everything from art songs to spirituals. She was magnificent in large choral works, such as Schoenberg’s Gurrelieder under Pierre Boulez in the Proms at the Albert Hall. But she was the go-to singer for the great public American occasion, notably the presidential inaugurations of Ronald Reagan (about which, as a Democrat, she had trepidation) and later Bill Clinton. There may not have been many operas for which Norman was the ideal choice, but she was in every sense a larger than life and irreplaceable artist.