Captain Bruce Bairnsfather (1888 - 1959) was a prominent UK humorist and cartoonist born at Murree, India, and educated at the United Services College, Westward, Ho. He studied to be an engineer but in 1914 rejoined the Royal Warwickshire Regiment and served in France until 1916, when he received a War Office appointment. His humorous black and white sketches of life in the trenches which appeared in Bystander made Bairnsfather's reputation.
Many of his cartoons from WWI in France were collected in Bullets & Billets[1]
He drew many of the early sketches for the advertisements for Beecham's Pills.
His character "Old Bill", popular between the World Wars, wore a large walrus moustache. Many policemen of the time had similar facial hair, and that may have led to British police being referred to as "The Bill".
Some of his cartoons are reproduced here