Which of the following spirits is essential for creating a classic Manhattan cocktail?

A classic Manhattan cocktail is traditionally made using rye whiskey, which is essential for its distinct flavor profile. Rye whiskey brings a spicy richness and complexity to the drink, which is crucial, as the Manhattan is known for its balance between the whiskey, sweet vermouth, and bitters. This spirit is not only traditional but also aligns with the drink's origins dating back to the late 19th century, where rye was a more commonly used whiskey in cocktails.

Using vodka, gin, or tequila would alter the fundamental character and taste of the Manhattan significantly. Vodka tends to be neutral and would lack the depth desired in this cocktail. Gin, while sometimes used in variations, does not align with the classic recipe, and tequila introduces a completely different flavor profile that does not complement the other ingredients in the way rye whiskey does. Thus, rye whiskey is the essential spirit for crafting a classic Manhattan.