Final answer:
Donato Bramante won the competition to design St. Peter's Basilica, which was later significantly contributed to by Michelangelo, including the design of the iconic dome.
Step-by-step explanation:
The competition for the design of St. Peter's Basilica, commissioned by Pope Julius II, was won by Donato Bramante in 1505. Bramante proposed a revolutionary centrally planned church with a Greek cross within a square and an imposing dome at the center. After Bramante's death, other architects like Raphael and Michelangelo made significant contributions to the basilica, with Michelangelo being credited with the final design of the colossal dome that dominates the basilica's skyline, although it remained unfinished at his death. Although other architects, such as Raphael and Michelangelo, made changes to Bramante's original plan, Bramante is credited with winning the competition and being the chief architect for St. Peter's Basilica.