Several of his early recordings were made in London, with noted producer George Martin.
John F. Kennedy | Pope John Paul II | Elton John | John | John Lennon | John Wayne | John McCain | John Kerry | John Cage | Olivia Newton-John | John Williams | John Peel | John Adams | John Steinbeck | John Travolta | John Milton | John Zorn | John Marshall | John Howard | John Singer Sargent | John Ruskin | John Updike | John Maynard Keynes | John Coltrane | John Cleese | St. John's | John Waters | John Lee Hooker | John Huston | John Ford |
O'Callahan has performed and recorded with John Langstaff and appeared several times in the character role of an ethnic storyteller in the Christmas Revels.
/The Greatest Sound Around, Eleanor Roosevelt, narrator (on Hello World!), words and music by Susan Otto and William R. Mayer, The Little Orchestra Society, Thomas Scherman, conductor, John Langstaff, tenor (on The Greatest Sound Around).