Final answer:
Cosimo de' Medici was the founder of the Medici dynasty, which rose to power in Florence through banking and politics, while also significantly contributing to the Renaissance through their patronage of the arts and founding of the Accademia dell'Arte del Disegno.
Step-by-step explanation:
The founder of the Medici dynasty was Cosimo de' Medici, who brought prominence to the Medici family in the Republic of Florence during the first half of the 15th century. This powerful banking family gained political power in Florence through the success of the Medici Bank, which was the largest bank in Europe at the time. The Medici's most significant contributions include their substantial patronage of the arts, sponsoring a variety of artworks and architectural projects during the Renaissance, including works by renowned artists such as Michelangelo and Leonardo da Vinci. Moreover, Cosimo de' Medici was also responsible for founding the Accademia dell'Arte del Disegno in 1563, illustrating the family's deep involvement in promoting the arts and culture in Florence and beyond.