What exactly was the black-winged deity of love? What secrets that masterwork uncovers about the rogue genius

A young boy screams as his head is forcefully held, a massive digit digging into his cheek as his parent's mighty hand grasps him by the neck. That scene from Abraham's Sacrifice appears in the Florentine museum, evoking unease through Caravaggio's chilling portrayal of the suffering child from the biblical account. It appears as if the patriarch, commanded by God to sacrifice his offspring, could break his neck with a single twist. However the father's preferred approach involves the silvery steel knife he grips in his remaining palm, ready to cut the boy's neck. One definite element remains – whoever modeled as the sacrifice for this breathtaking piece displayed extraordinary acting ability. There exists not only fear, shock and begging in his darkened gaze but also deep sorrow that a guardian could abandon him so utterly.

The artist took a well-known biblical story and made it so fresh and raw that its horrors seemed to unfold right in view of the viewer

Standing in front of the painting, viewers recognize this as a real countenance, an precise record of a adolescent model, because the identical youth – recognizable by his tousled hair and almost dark eyes – appears in two additional works by the master. In each case, that richly expressive face commands the scene. In John the Baptist, he gazes mischievously from the darkness while embracing a lamb. In Amor Vincit Omnia, he smirks with a toughness learned on the city's alleys, his black plumed appendages sinister, a naked adolescent creating chaos in a affluent residence.

Amor Vincit Omnia, presently exhibited at a London gallery, constitutes one of the most discomfiting artworks ever painted. Observers feel completely unsettled gazing at it. Cupid, whose arrows fill people with often painful longing, is shown as a very tangible, vividly illuminated unclothed form, standing over overturned objects that include stringed devices, a musical score, metal armor and an builder's ruler. This heap of items echoes, deliberately, the geometric and architectural gear strewn across the floor in Albrecht Dürer's engraving Melancholy – except here, the gloomy disorder is created by this smirking Cupid and the turmoil he can release.

"Love sees not with the eyes, but with the soul, / And thus is feathered Love depicted sightless," penned Shakespeare, shortly prior to this painting was created around the early 1600s. But Caravaggio's god is not blind. He stares straight at you. That countenance – sardonic and ruddy-cheeked, staring with bold confidence as he poses unclothed – is the identical one that screams in terror in Abraham's Test.

As Michelangelo Merisi da Caravaggio painted his three portrayals of the same unusual-appearing kid in Rome at the start of the seventeenth century, he was the most acclaimed religious painter in a metropolis ignited by Catholic revival. The Sacrifice of Isaac reveals why he was sought to decorate sanctuaries: he could adopt a scriptural narrative that had been depicted numerous times previously and make it so fresh, so unfiltered and physical that the horror seemed to be occurring immediately before you.

Yet there existed a different side to Caravaggio, apparent as soon as he arrived in the capital in the cold season that ended the sixteenth century, as a painter in his initial twenties with no mentor or supporter in the city, only skill and boldness. The majority of the paintings with which he caught the sacred city's eye were anything but holy. That could be the absolute first hangs in the UK's art museum. A young man parts his red mouth in a scream of agony: while reaching out his filthy fingers for a cherry, he has instead been attacked. Boy Bitten By a Lizard is eroticism amid poverty: observers can discern Caravaggio's dismal chamber mirrored in the murky liquid of the glass container.

The boy wears a pink blossom in his hair – a symbol of the sex trade in Renaissance painting. Venetian painters such as Titian and Palma Vecchio depicted courtesans holding flowers and, in a painting destroyed in the second world war but known through images, the master represented a famous woman courtesan, holding a bouquet to her bosom. The message of all these floral indicators is clear: sex for sale.

How are we to make of Caravaggio's sensual depictions of boys – and of one boy in specific? It is a inquiry that has split his interpreters since he gained widespread recognition in the twentieth century. The complicated historical truth is that the artist was not the queer icon that, for example, the filmmaker put on film in his 1986 film Caravaggio, nor so entirely devout that, as certain art historians improbably claim, his Boy With a Basket of Fruit is actually a portrait of Jesus.

His early paintings do offer overt sexual implications, or even offers. It's as if the painter, then a penniless youthful artist, identified with the city's sex workers, offering himself to live. In the Uffizi, with this idea in consideration, viewers might turn to another initial work, the 1596 masterpiece Bacchus, in which the god of wine stares coolly at the spectator as he begins to untie the black ribbon of his garment.

A few years following the wine deity, what could have driven the artist to create Victorious Cupid for the artistic patron the nobleman, when he was finally growing nearly respectable with prestigious ecclesiastical commissions? This profane non-Christian god revives the sexual provocations of his initial works but in a increasingly intense, unsettling way. Half a century later, its secret seemed obvious: it was a portrait of the painter's companion. A English visitor viewed Victorious Cupid in about the mid-seventeenth century and was told its figure has "the physique and countenance of [Caravaggio's|his] owne youth or assistant that laid with him". The name of this adolescent was Francesco.

The artist had been deceased for about 40 annums when this account was documented.