Bendor Grosvenor explains why Anthony van Dyck never resorted to a generic style of portraiture. Instead, his work was transformative at every stage of his career:

[E]ven at the age of 14 Van Dyck wanted to rewrite the rules of portraiture. And by 1623 he more or less had, to judge by his “Portrait of Cardinal Bentivoglio”, on loan to the Frick from the Palazzo Pitti in Florence. Painted in Rome shortly after Van Dyck had left Antwerp (and the employ of Rubens) to study the work of Italian artists such as Titian, “Cardinal Bentivoglio” was and still is regarded as a masterpiece of portraiture. Based on Titian’s “Portrait of Pope Paul III” but effortlessly surpassing it, Van Dyck makes Bentivoglio seem as alive as anyone ever has been on a piece of canvas.

Naturally, Bentivoglio is presented as rich and powerful, but he is never overwhelmed by the props that tell us who he is. His red cardinal’s robe is crumpled and lived-in, and above all is worn by a real person, not a mannequin, for Bentivoglio’s head is painted with such originality and deftness that we notice what he was like before we notice what he was. Although it is dangerous to believe we can see character in any portrait, Van Dyck’s Bentivoglio seems entirely like the man described by Cardinal Mazarin: “a sweet nature [with] noble thoughts, prudent, wise, experienced, witty, ingenious, and disinterested”. The picture has been sensitively restored for the exhibition.

Anthony van Dyck at the Frick Collection  (FT.com)