Ankaeus was the son of Poseidon as well as being the King of Samos.  Ankaeus was listed among the Argonauts.  When fellow Argonaut Tiphys who was the original helmsman died, Ankaeus took over the duty. This is told by Hyginus in Fabulae, 14


Poseidon and Astypalaea




While he was one of the Argonauts, the story of his death is the better known. Before leaving on the expedition with the Argonauts Ankaeus had planted a vineyard (Samos being well known for its wine). A seer told Ankaeus that he would never live to taste its wine. Despite all the dangers he and his fellow Argonauts faced, Ankaeus made it home safely by which time the grapes were ripe and had been made into wine. Ankaeus' return was to be celebrated before he drank his toast he had the seer come so he could mock the seer's prophecy. The seer replied "There is many a slip between the cup and the lip." Suddenly an alarm was sounded and word that a wild boar was ravaging the vineyard came. Ankaeus immediately dropped the cup and went out to investigate – and was promptly killed by the boar. As he had never had the chance to drink at his toast the prophecy was fulfilled.

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