in his work on the construction of Saint Peter's, Michelangelo's final design was a modification of the plan devised by which architect?

Donato Bramante

Explanation:

Donato Bramante was the first one selected to architect Saint Peter's Basilica and his design was inspired by the Pantheon.

The foundation stone was laid in 1506, but after Pope Julius died in 1513. the project was assigned to Giuliano da Sangallo and Fra Giocondo.

However, both of them (along with Bramante) died in the next few years. Afterwards, some work was done by Raphael, Baldassare Peruzzi, and Antonio da Sangallo the Younger, but the progress of the basilica wasn't too influencial.

Finally, at the beginning of 1547, Michelangelo took over as the principal designer.

He took ideas of the previous architects in great consideration, especially the original work of Bramante's. He kept the core of all his ideas and finally finished the design of Saint Peter's Basilica.