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
After Bramante's death in 1514, Raphael was named architect of the new St Peter's. Most of his work there was altered or demolished after his death and the acceptance of Michelangelo's design, but a few drawings have survived. It appears his designs would have made the church a good deal gloomier than the final design, with massive piers all the way down the nave, "like an alley" according to a critical posthumous analysis by Antonio da Sangallo the Younger. It would perhaps have resembled the temple in the background of "The Expulsion of Heliodorus from the Temple".