Dublin can't support more than one portrait painter, George Russell wrote to Lady Gregory in 1901, adding "now it is Walter Osborne". At the beginning of the 20th century, Osborne was indisputably Ireland's most fashionable portraitist, a position which would have remained his had he not died two months before his 44th birthday in April 1903.

Today, it is the artist's Belgian and French town-and-landscapes painted in the early 1880s, along with the views of Dublin and its surrounding countryside produced after his return to this country, which are most highly favoured by collectors. But certainly, during the latter part of his life, Osborne was held in esteem - and best paid - for his portraits. Of course, this particular genre has never been as admired as others, because portrait painters are frequently believed to have opted for a relatively easy means of making money.

This need not be the case: the best Irish portraitists such as John B Yeats (an artist whose exceptional talent has still not been properly recognised) bring very specific skills, not least psychological, to their work. The same is also true of Osborne. Some of his most attractive portraits are either of children on their own or feature mothers and children, the latter theme seemingly taken from the artist's study of Reynolds. Last year, for example, Christie's in London, sold Osborne's delightful Mrs Chadwyck-Healey and her Daughter Elizabeth for £331,500 sterling.

Painted in 1900, the picture was one of a series of similar works beginning four years earlier with Lady Brooke and her Daughter Emily and followed by Mrs Andrew Jameson and her Daughter Violet; the second of these was lampooned in Punch as The Torture Chamber, because the child's shoes had been nailed to the floor of Osborne's studio to make sure she kept the same pose. The most famous of this group was Mrs Noel Guinness and her Daughter Margaret, which won a bronze medal at the Paris International Exhibition of 1900 and was widely reproduced at the time. Portrait commissions have always been profitable, and it is relevant that Osborne only turned seriously to this form in the 1890s when he became financially responsible for his parents and family.

Nonetheless, he was a sufficiently fine, and conscientious, painter not to let the quality of work degenerate. The fact that he died relatively young no doubt also helped ensure standards were maintained; it is only in the latter part of their careers that other artists who came to specialise in portraits, such as Lavery and Orpen, allowed themselves to lapse into somewhat repetitive formulas. Born in Rathmines, Dublin in June 1859, Osborne was the son of a painter who specialised in animals. From youth, his abilities were recognised and by the age of 18 he was already exhibiting at the RHA. He was evidently a very charming man, and very popular with his patrons. But Osborne was also modest; when the Lord Lieutenant, Earl Cadogan, offered him a knighthood in 1900 for his services to art, he declined the honour. His early death from pneumonia, caused considerable dismay in Dublin.

"It has been a great shock to me," Hugh Lane wrote to Sarah Purser afterwards, "as he was one of our few geniuses and I hoped for still greater things from his brush." It may be that Lane, like other admirers of Osborne, felt he was rather wasting his talent by painting portraits. Stephen Gwynn, for example, felt that the artist's work in this field, "with all its technical dexterity, with all its charm of colour, lacked the essential gift . . . He was a little too courteous in the fibre of him ever to set down his impression of any other human being with entire unreserve."

Even during his lifetime there was something of a consensus that he responded better to female than male sitters, perhaps because the latter were so often intended as formal commissions in which there was not much opportunity for spontaneity of response on the part of the artist.

But a picture such as the portrait of Sir Walter Armstrong, now in the collection of the National Gallery of Ireland, is also worthy of study, probably because the subject was a friend of Osborne's. It is certainly true, as Jeanne Sheehy states in her 1983 monograph on the painter, that he was capable of producing "potboilers", but Osborne also created many wonderful portraits which show him at his finest.