In Greek mythology, Mopsus was the name of two famous seers:

Mopsus, son of Manto and Rhacius or Apollo

Mopsus, a celebrated prophet, son of Manto and Rhacius or Apollo. He officiated at the altars of Apollo at Claros ; and from his unerring wisdom and discernment gave rise to the proverb, "more certain than Mopsus". He distinguished himself at the siege of Thebes; but he was held in particular veneration at the court of Amphilochus, at Colophon in Ionia. Having been consulted, on one occasion, by Amphilochus, who wished to know what success would attend his arms in a war which he was going to undertake, he predicted the greatest calamities; but Calchas, who had been the soothsayer of the Greeks during the Trojan War, promised the greatest successes. Amphilochus followed the opinion of Calchas, but the prediction of Mopsus was fully verified. This had such an effect upon Calchas that he died soon after. His death is attributed by some to another mortification of the same nature. The two soothsayers, jealous of each other's fame, came to a trial of their skill in divination. Calchas first asked his antagonist how many figs a neighboring tree bore; ten thousand and one, replied Mopsus. The figs were gathered, and his answer was found to be true. Mopsus now, to try his adversary, asked him how many young ones a certain pregnant sow would bring forth, and at what time. Calchas confessed his inability to answer, whereupon Mopsus declared that she would be delivered on the morrow, and would bring forth ten young ones, of which only one would be a male. The morrow proved the veracity of his prediction, and Calchas died through the grief which his defeat produced. (Tzetz., ad Lycophr., 427.) Amphilochus subsequently, have occasion to visit Argos, entrusted the sovereign power to Mopsus, to keep it for him during the space of a year. On his return, however, Mopsus refused to restore to him the kingdom, whereupon, having quarreled, they engaged and slew each other. (Tzetz., ad Lycophr., 440). According to another legend, he was slain by Hercules. (Tzetz., ad Lycophr., 980).

Mopsus, the son of Ampyx and Chloris

A son of Ampyx and Chloris, born at Titaressa in Thessaly. He was the prophet and soothsayer of the Argonauts, and died at his return from Colchis by the bite of a serpent in Libya. (Hygin., fab., 14, 128, 172.? Tzetz., ad Lycophr., 980)

• This section includes text from Charles Anthon's A Classical Dictionary (1842).