Who was Caravaggio's dark-feathered god of love? The insights that masterwork uncovers about the rebellious artist

The youthful lad screams while his head is forcefully held, a large digit digging into his cheek as his father's powerful hand grasps him by the neck. That scene from Abraham's Sacrifice appears in the Uffizi Gallery, evoking unease through the artist's harrowing rendition of the tormented child from the scriptural account. The painting seems as if Abraham, instructed by God to sacrifice his offspring, could break his neck with a solitary turn. However the father's preferred approach involves the silvery grey knife he grips in his other palm, prepared to slit Isaac's neck. One certain element stands out – whomever modeled as Isaac for this astonishing piece displayed remarkable acting skill. Within exists not just dread, surprise and pleading in his shadowed gaze but also profound grief that a protector could abandon him so completely.

He adopted a well-known biblical tale and transformed it so vibrant and raw that its horrors seemed to happen right in front of you

Viewing before the artwork, observers identify this as a real countenance, an precise depiction of a adolescent subject, because the same boy – recognizable by his disheveled hair and almost black pupils – features in several additional works by the master. In every case, that richly emotional visage commands the scene. In John the Baptist, he gazes mischievously from the shadows while embracing a lamb. In Victorious Cupid, he grins with a toughness acquired on the city's streets, his dark feathery appendages sinister, a unclothed child running riot in a affluent residence.

Victorious Cupid, presently exhibited at a British gallery, represents one of the most discomfiting masterpieces ever painted. Viewers feel totally unsettled looking at it. The god of love, whose darts inspire people with frequently painful longing, is shown as a extremely tangible, brightly lit unclothed figure, standing over toppled-over items that include stringed instruments, a musical score, metal armour and an architect's ruler. This pile of possessions echoes, intentionally, the geometric and construction gear scattered across the ground in the German master's print Melencolia I – save here, the gloomy disorder is created by this grinning deity and the mayhem he can unleash.

"Love sees not with the vision, but with the mind, / And thus is winged Love painted blind," penned Shakespeare, just prior to this work was produced around 1601. But the painter's Cupid is not unseeing. He stares directly at you. That countenance – ironic and rosy-faced, staring with bold assurance as he poses naked – is the same one that shrieks in terror in Abraham's Test.

As the Italian master painted his three portrayals of the same unusual-looking kid in Rome at the dawn of the 17th century, he was the highly celebrated sacred artist in a metropolis enflamed by Catholic renewal. Abraham's Offering demonstrates why he was commissioned to decorate churches: he could adopt a biblical narrative that had been portrayed numerous times previously and make it so fresh, so unfiltered and visceral that the horror seemed to be happening directly in front of you.

Yet there was another aspect to the artist, apparent as soon as he came in the capital in the winter that concluded 1592, as a painter in his initial twenties with no mentor or supporter in the urban center, just talent and audacity. Most of the works with which he captured the sacred metropolis's attention were everything but devout. That may be the absolute earliest resides in London's National Gallery. A youth parts his crimson mouth in a scream of pain: while stretching out his filthy digits for a fruit, he has instead been attacked. Boy Bitten By a Lizard is eroticism amid squalor: viewers can see the painter's dismal chamber reflected in the murky liquid of the transparent vase.

The adolescent wears a rose-colored blossom in his coiffure – a emblem of the erotic commerce in early modern art. Northern Italian painters such as Tiziano and Palma Vecchio portrayed prostitutes holding flowers and, in a painting destroyed in the second world war but documented through photographs, Caravaggio represented a renowned woman prostitute, clutching a posy to her bosom. The message of all these botanical indicators is clear: intimacy for purchase.

What are we to make of Caravaggio's erotic portrayals of boys – and of one adolescent in specific? It is a question that has split his commentators since he achieved mega-fame in the twentieth century. The complicated past reality is that the painter was not the homosexual hero that, for example, Derek Jarman put on screen in his 1986 film Caravaggio, nor so entirely pious that, as certain artistic historians unbelievably assert, his Youth Holding Fruit is in fact a likeness of Christ.

His early paintings indeed offer overt sexual implications, or even offers. It's as if the painter, then a penniless young creator, identified with the city's prostitutes, selling himself to live. In the Florentine gallery, with this thought in mind, observers might turn to an additional early work, the sixteenth-century masterwork Bacchus, in which the god of alcohol stares coolly at the spectator as he starts to undo the dark sash of his robe.

A few annums after Bacchus, what could have driven the artist to paint Victorious Cupid for the art patron the nobleman, when he was at last growing almost established with prestigious ecclesiastical commissions? This profane non-Christian deity revives the erotic provocations of his early works but in a increasingly intense, uneasy manner. Fifty years afterwards, its secret seemed obvious: it was a portrait of the painter's companion. A English visitor viewed the painting in about 1649 and was told its subject has "the physique and countenance of [Caravaggio's|his] own youth or assistant that slept with him". The identity of this adolescent was Francesco.

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