Contrary to some beliefs that Bach invented it, the first organ, (called "the hydraulis"- a name due to the use of water reservoirs, which were used to stabilize air pressure in the windchests - not because it was a "water organ"!) was invented in the 3rd century B.C. by Ctesibius, a Greek genius who worked at the court of the Egyptian Pharaoh Ramses II!  This organ was certainly not used, as it is mostly today, in churches, but for the entertainment of the pharaoh and his guests.  It was a much smaller portable version, spanning only two octaves (versus five today) and only one keyboard (versus two to six today!)  Eventually it travelled, over the course of the next few centuries, first to Constantinople (today's Istanbul) and to Rome for similar purposes of pleasing the emperor's ears! 
     Then around 800 A.D.  it made its way to France, where Pepin, the French emperor, upon hearing its sounds, decided it was most fitted to praise the Lord and His Angels and installed one in the Church of St. Corneille in Compičgne outside Paris!  The organ grew in size (number of pipes and keyboards) and scope (expanding to many churches and cathedrals across Europe and later, North America!) 
     For those of you unaware of this history, the largest instrument ever built is right here in Center City Philadelphia in what was formerly called the Wanamaker Building across from City Hall.  Built by Rod and John Wanamaker, (the inventors and owners of the "world's first department store"), for the occasion of the 1910 World's Fair which was held in Philadelphia!  It is built inside the massive building (formerly the Philadelphia Central Train Station!) on nine stories and has over 55,000 pipes operated from an impressive console with six keyboards and 464 stop-registers!
     Some of the other renowned pipe organs (that yours truly has performed on many times) are in New York's St. Patrick's Cathedral and Riverside Church (where Virgil Fox played for over 40 years), Washington D.C.'s National Cathedral, San Francisco's St. Matthew's Cathedral, in Europe at Notre Dame Cathedral in Paris, Chartres Cathedral (also in France), London's St. Paul's Cathedral and Westminster Abbey, Vienna's St. Stephens Cathedral; and of course in Romania in the Black Church in Brasov (Transylvania), and last but not least the Cathedral of St. Joseph in Bucharest, my native city, where I had the privilege of being the organist and choir master for a number of years back in the seventies before coming to the USA!

     Regretfully, very few famous composers wrote pieces for the organ and orchestra.  Bach surprisingly did not write any (although his solo organ legacy is the most impressive of all).  Handel, on the other hand, wrote a handful (twelve), and Haydn wrote two (the F Major being performed by me this Sunday with the Camerata Ama Deus at Daylesford Abbey).  Mozart wrote some (called Church Sonatas for Organ and Strings) and later there were a few here and there (notably Francis Poulenc and Maurice Durufle). In spite of this and due to the majestic and varied sounds unique to it, the organ remains forever "the queen of the instruments"!