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.
Timoteo Viti
In 1503 Viti was painting banners for Cesare Borgia, who had expelled Duke Guidobaldo da Montefeltro as lord of the city. Guidobaldo regained Urbino in 1504 and Viti, along with Girolamo Genga, was commissioned by Bishop Arrivabene to decorate the chapel of S Martino in the cathedral. He continued to work successfully in the Marches for the rest of the decade, and as far south as Siena, where he and Genga collaborated on paintings in the Palazzo Petrucci in about 1508. 
Around 1514, Viti formed part of the large team assembled by Raphael and worked on the frescoes Raphael designed in the Chigi Chapel in Santa Maria della Pace in Rome. It has been suggested that he is depicted (as the Ancient Greek painter Protogenes) in "The School of Athens", Raphael's most famous work, standing next to Raphael's self-portrait, although Vasari does not mention this identification.