Bull-dog Drummond

Hugh 'Bulldog' Drummond, conceived in 1920, was the original daredevil adventurer and a prototype for all the slick sleuths which followed. McNeile himself having served in the Royal Engineers in the war, as well as being awarded the Military Cross, envisioned Drummond as a demobilized officer, who in the first novel gives an ad in the papers where he "welcomes diversion", because he's "finding peace incredibly tedious". There is only one condition: excitement essential