What characterizes a Dirty Martini compared to a Regular Martini?

A Dirty Martini is characterized by the inclusion of olive juice, which adds a distinct briny flavor to the cocktail. This ingredient sets it apart from a Regular Martini, which typically consists of gin or vodka and vermouth without the additional savory element. The olive juice not only enhances the taste but also slightly alters the appearance, giving the drink a murky or "dirty" coloration.

In contrast, options related to the amount of vermouth do not specifically define what makes a Dirty Martini unique, as verbiage regarding more or less vermouth relates to variations within regular Martini recipes rather than distinguishing a Dirty Martini. The option involving the use of whiskey is also unrelated, as traditional Dirty Martinis are made with gin or vodka. Thus, the defining characteristic remains the addition of olive juice, which crucially differentiates the Dirty Martini from its cleaner, more straightforward counterpart.