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 Villa Madama, a lavish hillside retreat for Cardinal Giulio de' Medici, later Pope Clement VII, was never finished, and his full plans have to be reconstructed speculatively. He produced a design from which the final construction plans were completed by Antonio da Sangallo the Younger. Even incomplete, it was the most sophisticated villa design yet seen in Italy, and greatly influenced the later development of the genre; it appears to be the only modern building in Rome of which Palladio made a measured drawing.