Petrus Sylvius (?)
The sitter’s flamboyant beret once led people to assume that he was a painter, for instance Gerard Dou or Ferdinand Bol, pupils of Rembrandt. However, he is probably Petrus Sylvius, a first cousin of Rembrandt’s wife, Saskia. Sylvius was a preacher, who was appointed to lead a  congregation in Friesland in 1637, and his departure may well have occasioned this portrait.