Gianfrancesco Penni
Born in Florence to a family of weavers, Penni entered Raphael's workshop very early in his life, and collaborated with him on several works, including the famous Rooms of the Vatican Palace, as well as the frescoes of Villa Farnesina, both in Rome. Heinrich Wölfflin and some other writers credited him with the entire execution of the Raphael Cartoons, with Raphael only creating the initial design, though more recent writers believe Raphael did much of the work himself.
Raphael
The main designs for the Villa Farnesina were not by Raphael, but he did design, and decorate with mosaics, the Chigi Chapel for the same patron, Agostino Chigi, the Papal Treasurer. Another building, for Pope Leo's doctor, the "Palazzo di Jacobo da Brescia", was moved in the 1930s but survives; this was designed to complement a palace on the same street by Bramante, where Raphael himself lived for a time.