Thousands of drinks are based off these original 7 Classics with a formula of spirit (any distilled, alcoholic liquid), sugar (a sweetener like sugar, honey, agave, etc), water (for dilution, most cocktails use ice as their water component), bitters (traditionally an alcoholic preparation flavoured with botanical matter). The end result is a bitter, sour, or bittersweet flavor - the salt & pepper of the drink world.
Important as these elements are, ice is the one that influences the glassware design the most.