When it comes to organ music, Johann Sebastian Bach is the gold standard. In addition to the work he did at Leipzig and Cõthen (pronounced much like curtain), Bach went around to various German cities as an organ consultant, evaluating new organs and telling the church authorities what needed to be improved. Like every organist throughout musical history, Bach was able to improvise freely and write down what he had just played. Bachs autograph scores show amazingly precise calligraphy. You can play the piece right off a Bach hand-written score.
The most popular of his organ pieces is the Toccata and Fugue in D minor, which had been arranged for a whole variety of instruments to include full orchestra. As a comment notes on the video, this is old school heavy metal.
Note that the organist requires a second person to handle the various stops on the organ. The camera also shows the complexity of the pedal work.
Bach: Toccata and Fugue in D minor