Harshvardhana, an ancient Indian emperor, was defeated by Pulakesin II. Pulakesin II was the ruler of the Chalukya dynasty and was known for his military prowess. Although the provided answer is generally correct, it is important to note that Harshvardhana faced other challenges and conflicts during his reign. For example, he had conflicts with Sasanka, the ruler of Gauda, but it can be argued that Sasanka did not directly defeat Harshvardhana. Additionally, Harshvardhana had friendly relations with Prabhakaravardhana, the ruler of Thanesar, and they even formed an alliance through marriage. Therefore, while Pulakesin II is the most prominent figure associated with Harshvardhana`s defeat, it is crucial to acknowledge the other historical complexities and interactions during that time period.