One of the legendary moments in Callas's career came in 1950 in Mexico City, when she interpolated a stupendous top E flat at the end of the Triumphal Scene in Act II of Aida. In this recording under Serafin she abided by the score, but still prompted Gramophone to speak of her 'fascinating art and prodigious personality', observing the way she was 'rapt in imaginative intensity in the significance of the words'.

The role of Nedda in Leoncavallo's verismo classic never entered Callas's stage repertoire, and so her recording made with the forces of La Scala, Milan, between 12 and 17 June 1954 represents one of her explorations of an opera made purely within the confines of the studio, rather than developing over a period on the stage. But as in all such cases - this was the first time she recorded a role she had not previously sung - Callas's desire to explore it to the fullest remains paramount. There is a complete identification between singer and character, down to the smallest detail, that make her Nedda an unusually complex creation that grows throughout the opera as she responds to its desperate emotional thrills and spills.

This is the first of Callas's two complete recordings of her signature role, the druid priestess Norma, in which she has remained unrivaled for 50 years. It captures her voice inits imposing early prime, while in the two famous duets for Norma and Adalgisa she is partnered by Ebe Stignani, generally considered the greatest Italian mezzo-soprano of her era. The conductor is Callas's mentor Tullio Serafin.

Relentlessly pursued by Fate, Leonora in La forza del destino is a haunted heroine whose passions and fears are expressed on a grand scale. Callas’s stage experience of Forza was limited to her early career in Italy – in fact, Leonora was her first Verdi role – but, as Lord Harewood, founder of Opera magazine, observed, her recorded assumption exhibited ‘an unparalleled musical sensibility and imagination and a grasp of the musico-dramatic picture which is unique’. She took her place in a powerful cast conducted by her mentor Tullio Serafin.

This Tosca, made in 1953 with the forces of La Scala, is a landmark in recording history.Conducted with searing intensity by Victor de Sabata, it teams Callas with two of her closest colleagues, the tenor Giuseppe di Stefano and the baritone Tito Gobbi - a performer who could rival Callas in dramatic finesse and power. Tosca's aria 'Vissi d'arte' (I lived for art) has come to be seen as Callas's personal manifesto.

Callas only sang Gilda in Rigoletto in one run of performances, in Mexico City in 1952, and she recorded the role three years later. She moves beyond the girlish tone and sparkling coloratura of the character's first scenes to create a figure of tragic stature as events unfold. 'Once heard, this rendering is never likely to be forgotten,' was Gramophone's judgement on her interpretation, and the same could apply to Tito Gobbi's, embodying every aspect of the accursed court jester.

The role of Leonora in Verdi's Il trovatore was one that Maria Callas performed some 20 times in the theatre, and this recording was her leave-taking of it. Callas's Leonora was praised by the critics for its vocal and dramatic artistry. Cecil Smith in Opera magazine said: "For once we heard the trills fully executed, the scales and arpeggios tonally full-bodied but rhythmically bouncing and alert, the portamentos and long-breathed phrases fully supported and exquisitely inflected".

Like Lucia di Lammermoor and Elvira (I puritani), Amina, the gentle heroine of La sonnambula,was a role that had become associated with light-voiced coloratura sopranos. Callas brought both a new substance and subtlety to the role when Luchino Visconti staged it for her at La Scala in 1955. This recording was made two years later, when the production was revived.

Until she achieved a triumph in the delicate coloratura role of Elvira in I puritani - in Venice in 1949 under the tutelage of maestro Tullio Serafin - Maria Callas had been making her name in dramatic roles, such as the epically scaled title role in Die Walküre, which she had been singing just days before. Her success in Bellini's final opera set her firmly on the path to bel canto supremacy. Joining her as Arturo in this 1953 recording is one of her best-loved colleagues, the tenor Giuseppe di Stefano.