"a ring with a cameo of Laocoön's head"

 Laocoön appears in Greek and Roman mythology. He was the Trojan priest of Poseidon who, in Homer's Iliad, utters the famous phrase, "Beware of Greeks bearing gifts" in reference to the Trojan Horse.

He is also remembered for the grisly manner of his death: sea-serpents sent by a god (some accounts say Athena, others Apollo or Poseidon) strangled him along with his sons.