Biography of Cosimo de' Medici, De Facto Ruler of Florence

The Florentine banker took his family's power to new heights

Portrait of Cosimo de' Medici, circa 1518
Portrait of Cosimo de' Medici by Jacopo Pontormo, circa 1518 (Image: Wikimedia Commons).

Cosimo de’ Medici (April 10, 1389–August 1, 1464) was a banker and politician in early Renaissance-era Florence. Although his power was unofficial, deriving mostly from his immense wealth, he was highly influential as the founder of the powerful Medici dynasty. The Medici family shaped much of Florentine politics and culture over several generations.

Fast Facts: Cosimo de' Medici

  • Known For: Florentine banker and Medici patriarch who transformed the de' Medici family into the de facto rulers of Florence and laid the groundwork for the Italian Renaissance
  • Born: April 10, 1389 in Florence, Republic of Florence
  • Died: August 1, 1464 in Careggi, Republic of Florence
  • Spouse: Contessina de' Bardi
  • Children: Piero di Cosimo de' Medici, Giovanni di Cosimo de' Medici, Carlo di Cosimo de' Medici (illegitimate)

Early Life

Cosimo de’ Medici was born Cosimo di Giovani de’ Medici, the son of Giovanni de’ Medici and his wife, Piccarda (née Bueri). He was a twin, along with his brother Damiano, but Damiano died soon after birth. Cosimo also had a younger brother, Lorenzo, who joined him in the family banking business in adulthood.

At the time of Cosimo's birth, the Medici were already a powerful banking family in Florence. Cosimo's father, Giovanni, founded the Medici Bank, following the dissolution of another Medici relative’s bank. The bank expanded, branching out from Florence to reach all the other major Italian city-states, including Rome, Venice, and Geneva. The Roman branch created ties to the papacy.

Even the Church wasn’t exempt from the power of Medici money. In 1410, Giovanni lent Baldassare Cossa the money to purchase the rank of cardinal. Cossa went on to become the antipope John XXIII, and he repaid the Medici family by putting the Medici Bank in charge of all papal finances. Cosimo inherited this influence and wealth from his family, which gave him a head start when he took the reins.

Priore of the Republic

1415 was an important year for Cosimo de' Medici. He was named the priore of the Republic of Florence, giving him even more power as one of nine Signoria who governed the city-state. Although the term length was short, the role helped him consolidate his power, and he later held a political post again as an ambassador.

The same year, Cosimo married Contessina de’ Bardi, the daughter of the count of Vernio. Prior to the Medici family's domination of the banking world, the Bardi clan had run one of the richest banks in Europe. The Bardi bank ultimately failed, but the Bardi were still influential and powerful, and the marriage was intended to cement an alliance between two of Italy’s most powerful families. The couple had two children: Piero, who would be the next Medici patriarch and was later known as Piero the Gouty, and Giovanni. Cosimo also had an illegitimate son, Carlo, by an enslaved Circassian named Maddalena; Contessina agreed to care for the child.

Medici Leader

Cosimo’s father, Giovanni, stepped back from the operations of the Medici Bank in 1420, leaving Cosimo and his brother Lorenzo to run it. Giovanni died in 1429, leaving his sons with immense wealth. Interestingly, the majority of this wealth came from the bank’s business in Rome; only about ten percent of it came directly from Florence.

As the head of the Medici clan, Cosimo’s power only increased. Florence was, officially, a representative form of government, governed by municipal councils and the Signoria. Although Cosimo claimed to have no political ambitions and only served when his name was drawn at random to serve a short term on the Signoria, he actually controlled much of the government through the Medici wealth. Pope Pius II was reportedly quoted as saying, “Political questions are settled in [Cosimo's] house. The man he chooses holds office... He it is who decides peace and war... He is king in all but name.”

Cosimo used his influence and wealth to improve Florence as a whole. He was a noted sponsor of poets, philosophers, orators, and artists, spending vast sums of money as a patron of art and thought. One of his lasting legacies was the Palazzo Medici, which included work by major artists of the era. He also financially supported Brunelleschi so that the architect could complete the Duomo, one of Florence’s most famous landmarks. In 1444, Cosimo founded the first public library in Florence: the library at San Marco.

Power Struggles and Balances

By the 1430s, Cosimo de' Medici and his family were the most powerful in Florence, which posed a threat to other influential families such as the Strozzi and Albizzi. Cosimo was imprisoned in 1433 after a failed bid to conquer the nearby Republic of Lucca, but he was able to negotiate down from imprisonment to a sentence of exile from the city. Despite some factions calling for his continued imprisonment or even execution, Cosimo was able to achieve his desired sentence.

Cosimo promptly moved, first to Padua and then to Venice. His brother Lorenzo came with him. Cosimo brought his banking business with him and gained the support of many along the way, garnering praise for accepting exile instead of continuing the tradition of bloody intra-city power struggles. Soon, so many people had followed Cosimo away from Florence that his exile had to be lifted in order to stop the exodus. Upon his return, he began working to quash the factional rivalries that had led to his banishment and that had plagued Florence for years.

In later years, Cosimo de' Medici also was instrumental in brokering a balance of power in northern Italy that allowed for the Italian Renaissance to flourish. He indirectly controlled Milan through the Sforza family, and although his interference wasn’t always popular, his political strategies were fundamental to keeping outside powers, such as France and the Holy Roman Empire, out of Italy. He also welcomed notable Byzantines into Italy, resulting in a resurgence of Greek arts and culture.

Final Years and Legacy

Cosimo de’ Medici died on August 1, 1464 at the Villa Medici in Careggi. He was succeeded as the head of the Medici family by his son, Piero, whose own son would come to be known as Lorenzo the Magnificent. After his death, the Signoria of Florence honored Cosimo with the title Pater Patriae, meaning “father of his country.” It was Cosimo who ensured that his grandson, Lorenzo, had a full humanistic education. Lorenzo later became the single greatest patron of Italian Renaissance art, culture, and thought.

Although Cosimo's descendants had an even larger influence, Cosimo de’ Medici laid the foundation that turned the Medici—and the city of Florence—into historical powerhouses.


  • “Cosimo de’ Medici: Ruler of Florence.” Encyclopaedia Britannica,
  • Kent, Dale. Cosimo De' Medici and the Florentine Renaissance: The patron's oeuvre. New Haven: Yale University Press, 2000.
  • Tomas, Natalie R. The Medici Women: Gender and Power in Renaissance Florence. Aldershot: Ashgate, 2003.
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Prahl, Amanda. "Biography of Cosimo de' Medici, De Facto Ruler of Florence." ThoughtCo, Aug. 28, 2020, Prahl, Amanda. (2020, August 28). Biography of Cosimo de' Medici, De Facto Ruler of Florence. Retrieved from Prahl, Amanda. "Biography of Cosimo de' Medici, De Facto Ruler of Florence." ThoughtCo. (accessed March 29, 2023).