This is an ancient Roman statue of Antinous (Ant/IN/oh/us), a youth of renowned beauty and the lover of the Emperor Hadrian. Antinous drowned in the river Nile and Hadrian was devastated. He found consolation by surrounding himself with portraits of his beloved. He also founded a city on the banks of the Nile in honour of Antinous, which he called Antinoopolis and which had a temple to Antinous. A festival was also founded to honour his memory. If you look closely at the left knee of the sculpture, you'll see that there's a join, and beneath it, the surface of the marble is smoother. At some point, the ancient statue had lost its lower left leg and half the right arm, and the new pieces were carved in the eighteenth century to complete it. At the time people did not like their ancient sculptures to look damaged, whereas nowadays, it's considered essential to leave them as they are, with the marks of the passage of time.