Born into a noble Italian family, Giovanni de Medici committed his first murder at the age of twelve and was twice banished from Florence for unruly behaviour by the age of thirteen. He became a mercenary captain in the employ of Pope Leo X in March 1516, and by 1520 he commanded his band of mercenaries.

His force was recognised as one of the best in Italy, and by 1525 it numbered over 3,000 soldiers. Medici became known as Giovanni of the Black Bands after he placed black stripes, or bars, on his coat of arms following the death of his sponsor, Pope Leo X. The use of this imagery gained de Medici the nickname ‘The Great Devil’.