Ebenezer Gryce, the detective introduced in Anna Katharine Green's The Leavenworth Case, is a marvelous character. According to mystery essayist Michael Sims, Gryce was the first series detective, a character who returns in later books to continue solving mysteries. Beyond that, some of his mannerisms and habits keep reappearing in later detectives.
Consider, for example, the question of Mr. Gryce's habit of never looking at the person to whom he was speaking:
"Mr. Gryce was a portly, comfortable personage with an eye that never pounced, that did not even rest - on you. If it rested anywhere, it was always on some insignificant object in your vicinity, some vase, inkstand, book or button. These things he would seem to take into his confidence, make the repositories of his conclusions, but you - you might as well be the steeple on Trinity Church, for all the connection you ever appeared to have with him or his thoughts. At present, then, Mr. Gryce was, as I have already suggested, on intimate terms with the door-knob."
That was Mr. Gryce in 1878. Fifty years later, in 1928, Agatha Christie, in The Mystery of the Blue Train, introduced us to Mr. Goby, a private investigator and friend of Hercule Poirot, who has his own visual peculiarities, as Randall Toye points out in The Agatha Christie WHO'S WHO:
[He] had never been known to address the human being he was working for directly. He selected always the cornice, a radiator, a television set, a clock, sometimes a carpet or a mat."
Mr. Goby returns several times in later books to investigate some point for Poirot - but still winds up talking to a point on the wall or an electric socket, but never to his employer. I cannot prove that Mr. Goby is the son (or grandson) of Ebenezer Gryce, but I do have my suspicions; old family habits die hard.