Until now, the Rotterdam portraitist Jan Daemen Cool was known in the literature only as the maker of a group portrait painted in 1653 of the governors and administrator of the Holy Ghost Hospital at Rotterdam, and of a portrait of Piet Hein, which is dated 1629. Closer scrutiny of his activities reveals that the artist, who never signed his work, was Rotterdam's leading portrait painter in the second quarter of the 17th century. Jan Daemen Cool was born in Rotterdam in 1589 or thereabouts. He may have studied with Michiel Jansz. van Mierevelt in Delft, where he married Agniesje Jaspersdr. in 1613 and was admitted to the guild in 1614. He probably returned to Rotterdam in 1614 and spent the rest of his life there. After his first wife's death in 1622 he married again in 1623, this time to Lijsbeth Cornelisdr., the widow of Lowijs Porcellis. Many archive records indicate that Cool was a very prosperous man. After the death of his second wife in 1652. he bought himself a place in the Rotterdam almshouse; he also pledged to paint a group portrait of the governors. He died in 1660. An important starting point in reconstructing the artist's oeuvre is the portrait of the governors of 1653 (cat.no. 28), the authorship of which is substantiated by archive records. However, the portrait of Piet Hein, painted in 1629 (cat.no. I, 1st version), attributed on the basis of the inscription on Willem Hondius' print, is not an authentic Cool but probably an old copy after a portrait which he had painted a few years earlier. A systematic investigation of Rotterdam portraits from the period between 1620 and 1660 has yielded a closely related group of portraits which may be regarded as the work of one man and which include the 1653 governors piece. Combining this information with additional data and further indications has facilitated the reconstruction of Jan Daemen Cool's oeuvre. Pride of place in that oeuvre is occupied by a group of four family portraits painted between 1631 and 1637 and now in the museums at Lille (cat.no. 4), Edinburgh (cat.no. 6), Rotterdam (cat.no. 16) and Brussels (cat.no. 19). Hitherto these portraits have usually been assigned to Jacob Gerritsz. Cuyp. They are all situated in a landscape and represent an important step in the development of this type of family group in Dutch portraiture. A series of portraits of individual sitters painted be-for 1640, including companion pieces, some them identifiable a people who lived in Rotterdam, arc entirely consistent in style and execution with the aforementioned g group portraits. Elements in the portrait of Johan van Yck with his wife and son, painted in 1632 (cat.no. 5), correspond very closely with these works, but there are also discrepancies which suggest cooperation with another painter or later overpaints. A series of individual portraits dating to 1640 - 1654 link the first group of paintings and the late governors piece, the composition of which is quite exceptional in the entire production of such paintings in 17th-century Holland. Here, as in his early family groups, the artist shows himself to be quite an adroit arranger of f gures. Although this painting and two others of 1654 clearly show that he continued to paint after enterning the almshouse, ture is no extant work from the last years of his life. Along the Rotterdam portraits of the rest ched period are a few - likewise unsigned - family groups which are strongly influenced by Cool but are obviously the work of a less proficient hand (figs. 5 and 6). Comparison with a signed portrait of 1649 (fig. 7) enables them to be assigned to the painter Isaack Adamsz. de Colonia (ca. 1611-1663), presumably a pupil of Cool's. Although the work of Jan Daemen Cool bears a resemblance to that of such artists as Michiel van Mierevelt and Jan Anthonisz. van Ravesteyn, his oeuvre has a distinctive character that is most in evidence in his group portraits. There are obvious correspondences with painters such as Jacob Gerritz. Cuyp of Dordrecht, to whom various works by Cool were hitherto attributed, and Willem Willemsz. van Vliet of Delft - artists who likewise developed their own characteristic styles.