Richard Green, in the catalogue to the exhibition Albert Moore and his Contemporaries held at Newcastle in 1972, dated the picture c.1884-5 and described it as follows: 'A pendant to no.62 [A Girl's Head, oil on canvas, 11½ x 9 1/8in., c.1884-5; private collection]. This painting is said to be a portrait of Ellen Terry, and is probably to be identified with Portia, one of two small oil paintings, Portia and The Blonde, which Moore exhibited at McClean's Gallery in 1885.'
Ellen Terry first made her mark as Portia in The Merchant of Venice at the Prince of Wales's Theatre in 1875, and her reputation was confirmed when she played the part to Irving's Shylock during their second season at the Lyceum Theatre, 1879-80. It remained one of her most famous roles, and she calculated that in all she had played it over a thousand times. For further information, see Edith Craig and Christopher St John (eds.), Ellen Terry's Memoirs, 1933, pp.140ff; and Laurence Irving, Henry Irving, 1951, Ch.XX.
Moore is not known to have been a devotee of the theatre, although his 'chief work' in 1868 was a large canvas entitled A Greek Play, painted to go above the procenium arch of the Queen's Theatre in Long Acre. It is tempting to think that he might have been introduced to Ellen Terry by his stage-struck pupil Graham Robertson, but Robertson, according to his own account in Time Was (p.139), did not meet the actress, who was to become one of his closet friends, until the winter of 1887.