He owns a revolver, which he never took out a licence for, as he saw it as a war souvenir rather than a firearm.
He had spent part of his life in India, and often bored others with his stories about those times.
In the ITV 2005 adaptation of the novel, Colonel Archie Easterbrook is played by Robert Pugh. The portrayal here is substantially different from the original novel. Here, Easterbrook had been thrown out of the army because he had been habitually drunk. He had even shot at a fellow officer during a drunken brawl. His wife had divorced him because of his drunkenness. They had a daughter, Laura Easterbrook, but he had not seen her for ten years.
Easterbrook hoped to achieve anonymity by settling in Chipping Cleghorn. His house, Miss Marple observed, was different from those typical of ex-army officers in that it was not decorated with photographs and military memorbilia. In Chipping Cleghorn, he met Sadie Swettenham. This forms a romantic side plot unique to this adaptation. Easterbrook and Sadie would exchange presents such as marrows and quinces. Sadie stole a leg of mutton from Little Paddocks to make a roast for him.
Sadie's son, Edmund, was jealous and possessive of her, and did not want her to develop a romantic relationship. This led Edmund to denounce Easterbrook to the police when he recognised that the pistol which killed Rudi Scherz had belonged to the Colonel. As a result, Easterbrook was forced to recount his entire backstory to the police.
At end of the movie, Mrs Swettenham and Colonel Easterbrook walk off arm in arm with Edmund, suggesting that the son had come to accept the romance.