Giuseppe Balsamo (2 June 1743 – 26 August 1795), known by the alias Count Alessandro di Cagliostro, was an Italian occultist, self-styled magician and confidence trickster. He became a glamorous figure associated with the royal courts of Europe where he pursued various occult arts, including psychic healing, alchemy, and scrying. In his 1833 essay, Count Cagliostro, Thomas Carlyle (1795–1881) pronounced him the "Quack of Quacks".

Cagliostro was born Giuseppe Balsamo on June 8, 1743 in Albergheria, Palermo, Kingdom of Sicily. Several sources, including Cagliostro himself, state that he was descended from the Byzantine Greek family of Komnenos; specifically the Megas Komnenos branch, which ruled the Empire of Trebizond. Given that 'Balsamo' is a name of Greek origin, and that Albergheria was largely inhabited by people of Greek descent, Cagliostro's claim to Greek ancestry seems valid. Albergheria was also known as the Jewish Quarter, which led later biographers to state that Cagliostro was at least part Jewish, despite the fact that he was from a Catholic family.

Cagliostro's parents were Pietro and Felicita Balsamo. Pietro, the son of a ribbon merchant, owned a prosperous shop and the Balsamos were described as "honest tradespeople". However, for unknown reasons, Pietro was forced to declare bankruptcy and died at age 45, leaving his wife to raise Giuseppe, one brother and one sister. Giuseppe, called 'Beppo', was taken under the wing of his godfather and maternal uncle, Giuseppe Cagliostro, after whom the boy was named and whose surname he would adopt. Cagliostro Senior saw the child's intelligence and wanted him to be educated for the Church. He placed him in the care of the Hospitallers at the Seminary of St Roch di Palermo. The boy repeatedly ran away; each time, he was "recaptured in vagabond company". Beppo was then sent to the Benedictine convent Santissimo Salvatore near Caltagirone, which had high walls and where he was forced to train as a novice. Here, it was discovered that he had an aptitude for natural history and herbalism. He was placed under the tuition of an apothecary, from whom he learned the first principles of chemistry and medicine. He was soon able to manipulate drugs, but it was noted that he was eager to "discover secrets which would further the interests of charlatanry". It was also noted that he had a "natural perversity", and an "innate viciousness". Beppo escaped from the convent and returned to Palermo, where he fell into a life of drunkenness, gambling, brawling and frequent arrests. The influential people of the city, who were friends of his family, interceded to keep him out of jail. He sold forged theatre tickets, stole from his uncle, committed extortion against a friend, and forged a will to help another party illegally obtain an inheritance. While he was a skilled artist, and earned money by giving drawing lessons, he was also skilled "at arms" and engaged in duels. All of this occurred before he had turned 15. In his neighbourhood, he was known as "Beppo Maldetto", or "Beppo the Cursed".

By age 17, the rogue, still using the name Giuseppe Balsamo, or Beppo Balsamo, had developed into an effective imposter, presenting himself as an initiate of the occult sciences. Handsome and haughty, and speaking little, Balsamo held others spell-bound. He had been seen evoking spirits and was believed to converse with angels. He attracted the attention of a superstitious goldsmith named Marano and told him of a treasure buried in an olive field. Balsamo told Marano that, through a ceremonial evocation, he could discover the precise location of the treasure. But, to carry out the ceremony, he needed 60 ounces of gold. Marano couldn't resist; he met Balsamo in the olive field, with the gold. Balsamo carried out the ceremony, to the extent that Marano was overcome by emotion. He fell to the ground, and Balsamo began to beat him with sticks. Balsamo left the goldsmith for dead and fled with the gold. By the time the goldsmith was delivered home and reported the incident to police, Balsano had sailed for nearby Messina. Messina was the home of an aunt, the sister of his uncle Giuseppe Cagliostro. She was very wealthy but Beppo discovered that she had recently died, and had left her money to charity. Still, he could benefit from her reputation and, under his own name, he was wanted by police. He changed his name and was, from then on, known as Count Alessandro Cagliostro.

In Messina, Cagliostro met a man known only as 'Althotas'. For some time, it was thought that Cagliostro had invented him, but an investigation by the Roman Inquisition proved his statements. Althotas was an alchemist, a chemist and a physician, fluent in several languages and educated, "in the entire circle of human sciences". It was agreed that Cagliostro would become his student. Over the next three years, the pair traveled throughout Egypt then, said Cagliostro, through "all the principal kingdoms of Africa and Asia", visiting and learning from priests and alchemists. Althotas claimed that he had discovered scientific methods of producing gold and precious stones; however it was achieved, they amassed a considerable sum of money. They also obtained letters of introduction to Manuel Pinto da Fonseca, Grand Master of the Order of Saint John, a powerful Portuguese nobleman who was infatuated with alchemy and who maintained his own laboratory at his home in Malta. Here, Cagliostro stated, Althotas died and his education was complete.

By this time, c. 1754 and age 21, Cagliostro had earned the respect of Pinto, who inducted him as a Knight of Malta, supplied him with money and sent him to Naples, accompanied by the Chevalier d'Aquino, of the Neapolitan House of Caramanica. Here, with a priest he had known in Palermo, he attempted to open a gambling house. This attracted negative attention from the Neapolitan government and Cagliostro left for France. Here, he presented himself as a pious man, occasionally wearing the garb of a priest. He visited churches and was often at the homes of cardinals; these connections produced letters of introduction which led him, c 1767, to Rome.

In Rome, Cagliostro moved into the Antico Albergo del Sole al Pantheon (Hotel of the Sun). He made small sums by selling 'art' (cheap drawings dressed up to appear valuable). He dressed well and presented himself as a man of noble birth. By now, his appearance had become less attractive—Carlyle describes him as a "dusky, bull-necked, mastiff-faced, sinister-looking individual". But when he met and fell in love with a beautiful 14-year-old girl named Lorenza Seraphinia Feliciani (c. 8 April 1751 – 1794), known as "Serafina", his presentation was enough to impress her father, who allowed them to marry in 1768. The couple lived with her parents but, as Lorenza would testify, Cagliostro immediately began to teach her how to attract men and, in the most lacivious fashion, gratify them. This led to quarrels with her parents and the couple had to move to their own house. From there, Serafina was forced to "entangle" men with sexual favours, with her husband assuring her that adultery was no crime if it was used to advance a woman's interests. Also from that house, with two other men, Cagliostro made large sums of money by forging bills of exchange. They were eventually caught and had to flee Rome.

From then on, Cagliostro and Serafina spent years traveling. They tried to settle in Bergamo but Cagliostro's identity was discovered; they were briefly jailed then stripped of their funds and expelled from the city. They went through Galicia, to Genoa, then Antibes, Barcelona, Madrid and Lisbon, living on the proceeds of Serafina's prostitution and Cagliostro's various scams, which included the sale of 'amulets' and 'cures'. In 1776, they reached London, by which time they were financially comfortable. Here, Cagliostro made an enemy of the blackmailer Charles Théveneau de Morande, who was also the editor of Le Courier de l'Europe, a highly-influential Franco-British newspaper. Cagliostro saw the newspaper as a means of advancing his interests; de Morande, who knew all about Cagliostro's history, attempted to extract funds from him and was rebuffed. de Morande began exposing Cagliostro in print, making sure that everyone in Europe knew who and what he was. This exposure availed nothing; Cagliostro continued to be welcomed by the illustrious people of the day.