Betty Grable was an American actress in the 20th century, known for her beautiful legs.
When Paris, playing the role of Bobby (an american soldier) from a holoprogram set in 1944 encountered Harry Kim in a corridor of the USS Voyager in 2374, Bobby asked him what part of Betty Grable he'd stare at to test him; Kim answered correctly just in time. (VOY: "The Killing Game, Part II")