Final answer:
Peter Paul Rubens was the Baroque painter who was an ambassador, diplomat, and court painter. Rubens had assistants who worked on different parts of a painting, and he influenced portraiture through his student Anthony Van Dyck.
Step-by-step explanation:
The Baroque painter who was an ambassador, diplomat, and court painter to dukes and kings, and supervised a huge workshop of assistants was Peter Paul Rubens.
Rubens spent several years in Italy studying Italian Renaissance art and the art of classical antiquity. He combined this with the influence of Caravaggio and the Venetian artists of the Renaissance. Rubens set up a large studio in Antwerp and had assistants working for him who specialized in different things, allowing them to work on different parts of a single painting.
Although Rubens was known for his religious and mythological paintings, he also had an influence on portraiture through his student Anthony Van Dyck, who became the court painter for Charles I of England.