[1] Keen was an early collaborator with the director Alfred Hitchcock, starring in his silent films The Mountain Eagle, The Lodger and The Manxman.

[4] In April 1927, Keen appeared in Packing Up, a short film made in the DeForest Phonofilm sound-on-film process.

[5] Keen was the father of actor Geoffrey Keen, and the two both played Iachimo in Cymbeline opposite Peggy Ashcroft: Malcolm at the Old Vic in 1932, Geoffrey at the Shakespeare Memorial Theatre in 1957.

[6][7][8] Keen played the Caliph in a production of James Elroy Flecker's Hassan at His Majesty's Theatre in London in 1923.

[9] Incidental music for the play was by Frederick Delius, and the ballet in the House-of-the-Moving Walls was created by Fokine.