Italian painter of the Sienese School during the early Renaissance. He was first mentioned on 24 May 1418, when he was paid for painting book covers (untraced) for biccherne (Sienese official records). He was a pupil of Taddeo di Bartolo, with whom he jointly signed an altarpiece (1420; untraced) in the Marescotti chapel (Siena, Sant'Agostino). He became Taddeo's partner on 25 October 1421 and was named in his will as his adoptive son and heir (August 1422). In 1422 he was one of the advisers on the construction of the church and loggia of San Paolo, Siena. On 11 April 1423 Gregorio married Jacopa, daughter of the Sienese sculptor Domenico di Niccolò dei Cori (1363-1453). The polyptych of the Madonna of Humility with Sts Augustine, John the Baptist, Peter and Paul (Siena, Museo dell'Opera del Duomo), signed and dated 1423, was made for Siena Cathedral and is Gregorio's only securely attributed work. Although the figure style and decorative elements owe much to Taddeo di Bartolo, Gregorio's style is more refined, brittle and elegant and his colour more delicate and clear than his master's. It has been suggested that he polychromed the wooden statue of the Virgin and Child (the 'Virgin of the Magnificat'; Siena, Sant'Agostino), attributed to Francesco di Valdambrino. Also attributed to Gregorio are a Crucifixion (Siena, Museo dell'Opera del Duomo), a Birth of the Virgin (Rome, Pinacoteca Vaticana), a Marriage of the Virgin (London, National Gallery, 1317), a Crucifixion (Avignon, Musée du Petit Palais) and a St Louis of Toulouse (Siena, Pinacoteca Nazionale). //