Baroque art emerged in the late sixteenth century as part of the counter-reformation. which artist's work marked the beginnings of baroque art?

Well, it depends on where you look for information.
Michelangelo created some works which are considered to be the beginnings of Baroque, although he was a Renaissance artist.
On the other hand, Gian Lorenzo Bernini is credited with creating the Baroque style of sculpture, so the answer is one of these two artists. 

If he tries to grape you then get a grape and grape him back

Answerminuet;