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.
The Prophet Isaiah (Raphael)
Much comparison is made of the Raphael fresco "Prophet Isaiah" to the work of Michelangelo, Ernst Gombrich going as far to suggest that Michelangelo may have hired Raphael to work on Ezekiel for the Sistine Chapel, which he believes is much more reflective of Raphael than of Michelangelo. This would have allowed Raphael to both gain influence by Michelangelo and also contribute to the decoration of the Sistine Chapel.