Gerre Hancock (1934-2012) was an American organist, composer, and one of the great masters of improvisation on the organ.
Here is a recording of Gerre Hancock improvising on the organ. It is one of a series of nine improvisations that is part of a program called “Praise the Eternal Light.” The improvisations were inspired by the cathedral windows of the Cathedral of St. Joseph in Hartford Conneticut where Gerre played for these recordings.
The recording of the improvisations is available from the webstore at http://www.proorgano.com. Search for item #7233 and you will find it.