Hugh Etherianus, or Ugo Eteriano[1] (1115–1182), was an adviser on western church affairs to Byzantine emperor Manuel Comnenus.
Nothing is known of his family apart from a letter sent after his death by the Pope to his brother Leo, nicknamed Tuscus, which mentions a "nephew", possibly Hugh's son.
He is notable for his work Contra Patarenos ("Against the Patarenes") which is a treatise against Catharism surviving in two Latin manuscripts in Oxford and Seville.
Hugh, who does not seem to have held any official post at court, but was a very learned theologian, had many opportunities of discussing the questions at issue between the Greek Orthodox Church and Catholics.
[5] As a result of these disputes he wrote a work in three books: De haeresibus quas Graeci in Latinos devolvunt, sive quod Spiritus Sanctus ex utroque Patre et Filio procedit.
It appears that the emperor, who was well disposed towards Latins, had suggested that he should write it, having asked him whether they have "any authorities of saints who say that the Holy Ghost proceeds from the Son".
There are also some incorrect expressions noted by the later editors, such as that God the Father is the cause of the Son (this is a concession to the Greeks that was, however, tolerated by the Council of Florence).