The organ (from Greek όργανον) is a keyboard instrument of one or more divisions. Each keyboard instrument is typically operated by either the hands or the feet.
The organ is a relatively old instrument that dates back to the time of Ctesibius of Alexandria, the man who is credited with the invention of the hydraulis. The organ was not a particularly popular instrument in the medieval church, but after the time of the Age of Exploration organs were increasingly found in liturgy services.
Archbishop Athenagoras Spyrou, who took over the Greek Archdiocese in 1931, was a big fan of organs and he encouraged their use in America. While he encouraged their use, it is likely that they had already become relatively common before 1931.
In George Anastasiou’s “Αρμονικη Λειτουργικη Υμνωδια,” Anastasiou claims to be the originator of organs in Greek Orthodox churches. In a paragraph appropriately titled “Organ Introducer” he says:
"I am convinced that I first introduced the organ in our Churches in America with the musical cooperation of ever-memorable artist and musical [sic] Spyridon Saphrides upon my arrival in America and my appointment as precentor-choir leader of the Greek Church of St. Sophia in Washington at the time of the progress and reformatory presidency of Mr. T. H. Theotokatos, lawyer and at that time teacher of this community in the year 1921. Later I introduced it also in New York and in other places by special musical-historic lectures, descriptions in our Greek press, and by special teaching in the choirs of our communities, which I formed, and lately in the beloved Greek city of Florida, Tarpon Springs, where there is played today, in that very beautiful cathedral church of America (as it is called today by all the Greeks and Americans by reason of the Pan-American celebration of Theophany services every year) an organ of great value electrically, microphonically, megaphonically, and with chimes, on the great singing tower, the bell tower of about 100 feet in height of this Greek Church of St. Nicholas in Florida, called the Greek singing Tower of America."
It is uncertain why organs were introduced to churches in America, but it may represent an attempt to "Westernize."