A passenger who gives unasked-for and usually unwanted advice to the driver of a vehicle; by extension, anyone who interferes without having real responsibility or authority. The term originated in the United States during the 1920s, when many automobiles were chauffeur-driven and their passengers sat in the backseat, often quite legitimately telling the chauffeur where to go. Today the passenger’s location is irrelevant, the term being principally figurative. It has largely replaced the older armchair general. See also Monday-morning quarterback and the very different take a backseat.

In control. The analogy here is obvious, but the actual expression did not become common until the nineteenth century. Lord Beaverbrook is quoted (New Statesman, 1963) as saying of David Lloyd George, “He did not care in which direction the car was travelling, so long as he remained in the driver’s seat.” See also in the saddle.