This is Lycurgus, entangled in the vine, inv. 844, from 4th century Harbiye.

From the Internet I gathered a legend about Dionysus: "When grown up, he discovered vine and its use, but was struck with madness by Hera. He wandered through Egypt and Syria before reaching Phrygia, where the goddess Cybele purified him and initiated him to her cult. Then, he went to Thracia where the local king, Lycurgus (not to be confused with the legislator of Sparta) refused to let him pass through his kingdom and tried to capture him. Dionysus took refuge in the sea near the Nereid Thetis, and Lycurgus, who had managed to capture Bacchæ accompanying Dionysus (whose other name is Bacchus), was struck with madness while the Bacchæ were miraculously freed, and, with an axe, killed his own son that he had mistaken for a vine. Lycurgus recovered his reason but his country had become sterile and, following an oracle, his people had to put him to death to stop the malediction, which they did by having him torn apart by four horses."