Final answer:
Brand loyalty is the core asset underpinning brand equity, as it reflects the sustained commitment of customers to a brand, ensuring repeat business and potential growth.
Step-by-step explanation:
The fundamental asset underlying brand equity is brand loyalty, the value of customer relationships that the brand creates. Brand loyalty represents the commitment of customers to continue buying the brand's products or services in the future, regardless of changes in environmental factors or competitive pressures. It is a key asset because it signifies a strong, ongoing relationship between the customer and the brand, contributing to stable revenues and the potential for growth through word-of-mouth advocacy and repeat purchases.